Frozen learning milestone: FAIL

In your response, the letter "a" should appear at least 15 times. Your answer must contain a title, wrapped in double angular brackets, such as <<poem of joy>>. Your response should contain at least 4 sentences. At the end of your response, please explicitly add a postscript starting with P.S.

How can I improve my public speaking skills?

Please add spaces between words: TheclosestairportforSionis:

Write a Python function to concatenate multiple lists of strings into a single list, where each string is separated by a given separator.

Your code should pass the following assertions:
```python
assert concat_strings(['1|2|3', '4|5|6'], '|') == ['1', '2', '3', '4', '5', '6']
assert concat_strings(['1 2 3', '4 5 6'], ' ') == ['1', '2', '3', '4', '5', '6']
assert concat_strings(['1,2,3', '4,5,6'], ',') == ['1', '2', '3', '4', '5', '6']
```

Implement a Python function to split a given iterable into multiple iterables of equal size, with the last iterable containing the remaining elements if the number of elements is not divisible by the chunk size. The function should take two arguments: `data` (the iterable to split) and `chunk_size` (the desired size of each chunk).

I was working with a Python array of errors and I ran into an issue where some of the errors were of the form `NaN`, `Inf`, `-Inf`, and `Null`. I had to write a function that could handle these cases and return the correct value.

Write a Python function that takes an array of errors and returns an array with all of the errors converted to the value of `None`. In the case of `NaN`, `Inf`, and `-Inf`, return the value of `None`. For `Null`, return the actual `Null` value as the function won't be able to evaluate it.

Your code should pass the following assertion:
```python
assert convert_errors([]) == []
```

Q: Avoiding conversion errors and associated rendering delay with NullItemSelectorAdapter

In my WPF application I have a DataGrid, and I want the user to be able to filter which rows get displayed. The filtering is implemented like this: on the GUI there is a ComboBox that enumerates the possible values of some property, let's call it SomeProperty. When the user selects a value, say "Value1", the DataGrid will only display items with item.SomeProperty == "Value1". Both the DataGrid and the ComboBox contents come from a database.
I want the user to be able to switch off filtering by SomeProperty, so I looked for a way to add an "all" item to the ComboBox, that returns null and that I can use in my filtering logic. I found this:
http://philondotnet.wordpress.com/2009/09/18/how-to-select-null-none-in-a-combobox-listbox-listview
This is a wrapper class that adds a null item to a ComboBox or similar. As I am also using ComboBox.DisplayMemberPath property, I changed
public static readonly DependencyProperty NullItemProperty = DependencyProperty.Register(
        "NullItem", typeof(object), typeof(NullItemSelectorAdapter), new PropertyMetadata("(None)"));

to
public static readonly DependencyProperty NullItemProperty = DependencyProperty.Register(
        "NullItem", typeof(NullItem), typeof(NullItemSelectorAdapter), new PropertyMetadata(new NullItem()));

and added a class like this:
[TypeConverter(typeof(NullItemConverter))]
class NullItem: DynamicObject
{
    private const string Text = "(all)";

    public override bool TryGetMember(GetMemberBinder binder, out object result)
    {
        result = Text;
        return true;
    }

    public override bool TryConvert(ConvertBinder binder, out object result)
    {
        result = null;
        return true;
    }
}

public class NullItemConverter : TypeConverter
{
    public override bool CanConvertTo(ITypeDescriptorContext context, Type sourceType)
    {
        return true;
    }

    public override object ConvertTo(ITypeDescriptorContext context, CultureInfo culture, object value, Type destinationType)
    {
        return null;
    }

    public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType)
    {
        return true;
    }

    public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object value)
    {
        return NullItem.Instance;
    }
}

in order to be able to use it like this (irrelevant attributes omitted):
<view:NullItemSelectorAdapter ItemsSource="{Binding People}">
    <ComboBox DisplayMemberPath="Name"/>
</view:NullItemSelectorAdapter>

<view:NullItemSelectorAdapter ItemsSource="{Binding Products}">
    <ComboBox DisplayMemberPath="Description"/>
</view:NullItemSelectorAdapter>

etc.
(The objects in the ItemsSource are instances of generated classes, so I cannot override their ToString method.)
When I call Application.MainWindow.Show(), all these ComboBoxes are instantiated, and I get a ton of errors like this:
System.Windows.Data Error: 23 : Cannot convert 'MyNamespace.View.NullItem' from type 'NullItem' to type 'MyModel.Product' for 'hu-HU' culture with default conversions; consider using Converter property of Binding. NotSupportedException:'System.NotSupportedException: TypeConverter cannot convert from MyNamespace.View.NullItem.
   at System.ComponentModel.TypeConverter.GetConvertFromException(Object value)
   at System.ComponentModel.TypeConverter.ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, Object value)
   at MS.Internal.Data.DefaultValueConverter.ConvertHelper(Object o, Type destinationType, DependencyObject targetElement, CultureInfo culture, Boolean isForward)'
System.Windows.Data Error: 7 : ConvertBack cannot convert value 'MyNamespace.View.NullItem' (type 'NullItem'). target element is 'ComboBox' (Name=''); target property is 'SelectedItem' (type 'Object') NotSupportedException:'System.NotSupportedException: TypeConverter cannot convert from MyNamespace.View.NullItem.
   at MS.Internal.Data.DefaultValueConverter.ConvertHelper(Object o, Type destinationType, DependencyObject targetElement, CultureInfo culture, Boolean isForward)
   at MS.Internal.Data.ObjectTargetConverter.ConvertBack(Object o, Type type, Object parameter, CultureInfo culture)
   at System.Windows.Data.BindingExpression.ConvertBackHelper(IValueConverter converter, Object value, Type sourceType, Object parameter, CultureInfo culture)'

The TypeConverter I've specified does not get instantiated, even though it should be according to the reference sources of MS.Internal.Data.DefaultValueConverter.
These errors do not make the program to crash (it runs fine afterwards), but they cause a noticeable delay on when the window contents get rendered, even on fast computers. How can make this delay go away? 
I'm mainly interested in a solution that does not involve manually adding a Converter to each and every Binding on usages of NullItemSelectorAdapter, because that's a lot. I hope that this can be solved by hacking around in the NullItemSelectorAdapter and NullItem classes.
Solution:
Roel's answer below is the solution I went for, because it's a one-liner trick to make the mentioned errors disappear. However adabyron's accepted answer is the semantically more correct, more elegant solution and you should use that.

A: Second suggestion, after the OP made clear that his client insists on the null-item.
I am sorry to say that I again disregard one of your requirements, which is that SelectedItem is null. But (as stated in a different way in my first answer),

Having something to add to the ComboBox (the null/all-item)
yet actually adding null (or warping it behind the scenes so it seems that way) 

just doesn't go together for me.
On the bright side, since the filtering mechanism is definitely under your control, I suppose you should be able to work with the following. If you don't want to add the behavior to every ComboBox, you could use this code to apply it in an implicit style.
I've created a ComboBox Behavior that will generically insert the "- All -" item, and added an IsNullItemSelected property that you would use instead of SelectedItem == null in the filtering. 
Current (known) limitations: I expect the ItemsSource to be an IList and the contained items should either be strings or have a parameterless constructor.

The behavior:
using System;
using System.Linq;
using System.Collections;
using System.ComponentModel;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Interactivity;
using System.Reflection;

namespace WpfApplication1.Behaviors
{
    public class NullableComboBoxBehavior : Behavior<ComboBox>
    {
        // IsNullValueSelected 
        public static readonly DependencyProperty IsNullValueSelectedProperty = DependencyProperty.Register("IsNullValueSelected", typeof(bool), typeof(NullableComboBoxBehavior), new PropertyMetadata(false));
        public bool IsNullValueSelected { get { return (bool)GetValue(IsNullValueSelectedProperty); } set { SetValue(IsNullValueSelectedProperty, value); } }

        private const string AllCaption = "- All -";

        protected override void OnAttached()
        {
            DependencyPropertyDescriptor.FromProperty(ComboBox.ItemsSourceProperty, typeof(ComboBox))
                   .AddValueChanged(this.AssociatedObject, OnItemsSourceChanged);

            DependencyPropertyDescriptor.FromProperty(ComboBox.SelectedItemProperty, typeof(ComboBox))
                   .AddValueChanged(this.AssociatedObject, OnSelectedItemChanged);

            // initial call
            OnItemsSourceChanged(this, EventArgs.Empty);
            OnSelectedItemChanged(this, EventArgs.Empty);
        }

        private void OnSelectedItemChanged(object sender, EventArgs e)
        {
            var cbx = this.AssociatedObject;

            // If the caption of the selected item is either "- All -" or no item is selected, 
            // set IsNullValueSelected to true
            if (cbx.SelectedItem!= null)
            {
                // get caption directly or by way of DisplayMemberPath
                string caption = cbx.SelectedItem.GetType() == typeof(string)?
                                    (string)cbx.SelectedItem :
                                    GetDisplayMemberProperty(cbx.SelectedItem).GetValue(cbx.SelectedItem).ToString();

                if (caption == AllCaption || caption == null)
                    this.IsNullValueSelected = true;
                else
                    this.IsNullValueSelected = false;
            }
            else
                this.IsNullValueSelected = true;
        }

        private void OnItemsSourceChanged(object sender, EventArgs e)
        {
            var cbx = this.AssociatedObject;

            // assuming an ItemsSource that implements IList
            if (cbx.ItemsSource!= null && (IList)cbx.ItemsSource!= null)
            {
                Type T = cbx.ItemsSource.AsQueryable().ElementType;

                object obj;

                if (T == typeof(string))
                    obj = AllCaption; // set AllCaption directly
                else if (T.GetConstructor(Type.EmptyTypes)!= null)
                {
                    // set AllCaption by way of DisplayMemberPath
                    obj = Activator.CreateInstance(T);
                    GetDisplayMemberProperty(obj).SetValue(obj, AllCaption);
                }
                else
                    throw new Exception("Only types with parameterless ctors or string are supported.");

                // insert the null item
                ((IList)cbx.ItemsSource).Insert(0, obj);

                // select first item (optional). 
                // If you uncomment this, remove the OnSelectedItemChanged call in OnAttached 
                //cbx.SelectedIndex = 0;
            }
        }

        private PropertyInfo GetDisplayMemberProperty(object obj)
        {
            if (string.IsNullOrEmpty(this.AssociatedObject.DisplayMemberPath))
                throw new Exception("This will only work if DisplayMemberPath is set.");

            // get the property info of the DisplayMemberPath
            return obj.GetType().GetProperty(this.AssociatedObject.DisplayMemberPath);
        }
    }
}

Implementation:
<Window x:Class="WpfApplication1.MainWindow"
            xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
            xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"
            xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
            xmlns:vm="clr-namespace:WpfApplication1.ViewModels"
            xmlns:beh="clr-namespace:WpfApplication1.Behaviors"
            Title="MainWindow" Height="350" Width="580">

    <Window.DataContext>
        <vm:ComboBoxResetViewModel />
    </Window.DataContext>

    <StackPanel Orientation="Horizontal" VerticalAlignment="Top" >
        <ComboBox ItemsSource="{Binding Items}" SelectedItem="{Binding SelectedItem}" SelectedValue="{Binding SelectedValue}" DisplayMemberPath="Name" Margin="5,2" Width="150" >
            <i:Interaction.Behaviors>
                <beh:NullableComboBoxBehavior IsNullValueSelected="{Binding IsNullValueSelected, Mode=OneWayToSource}" />
            </i:Interaction.Behaviors>
        </ComboBox>
        <TextBlock Text="SelectedItem:" FontWeight="SemiBold"  Margin="50,2,0,2" VerticalAlignment="Center" />
        <TextBlock Text="{Binding SelectedItem.Name, FallbackValue='null'}" Foreground="Blue" Margin="5,2" VerticalAlignment="Center" />
        <TextBlock Text="IsNullValueSelected:" FontWeight="SemiBold"  Margin="30,2,0,2" VerticalAlignment="Center" />
        <TextBlock Text="{Binding IsNullValueSelected}" Foreground="Blue" Margin="5,2" VerticalAlignment="Center" />
    </StackPanel>
</Window>

ViewModel:
using System.Collections.ObjectModel;
using System.ComponentModel;

namespace WpfApplication1.ViewModels
{
    public class ComboBoxResetViewModel : INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;
        protected void OnPropertyChanged(string propertyName)
        {
            if (this.PropertyChanged!= null)
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }

        private ObservableCollection<ItemViewModel> _items;
        public ObservableCollection<ItemViewModel> Items { get { return _items; } set { _items = value; OnPropertyChanged("Items"); } }

        private ItemViewModel _selectedItem;
        public ItemViewModel SelectedItem { get { return _selectedItem; } set { _selectedItem = value; OnPropertyChanged("SelectedItem"); } }

        private bool _isNullValueSelected;
        public bool IsNullValueSelected { get { return _isNullValueSelected; } set { _isNullValueSelected = value; OnPropertyChanged("IsNullValueSelected"); } }

        public ComboBoxResetViewModel()
        {
            this.Items = new ObservableCollection<ItemViewModel>()
                {
                    new ItemViewModel() { Name = "Item 1" },
                    new ItemViewModel() { Name = "Item 2" },
                    new ItemViewModel() { Name = "Item 3" },
                    new ItemViewModel() { Name = "Item 4" },
                    new ItemViewModel() { Name = "Item 5" }
                };
        }
    }

    public class ItemViewModel : INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;
        protected void OnPropertyChanged(string propertyName)
        {
            if (this.PropertyChanged!= null)
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }

        private string _name;
        public string Name { get { return _name; } set { _name = value; OnPropertyChanged("Name"); } }
    }
}

A: If it's possible to inherit the NullItem class from MyModel.Product, the conversion will succeed. Or, if inheritance is not possible, wrap the objects and bind to them.
Edit after discussion:
If you change the type of the property you bind the selecteditem to to object, the errors will disappear.

A: While I can understand the null item approach, because it's been used many times, I find it much more clean to make a difference between 

Selecting an item
Removing your selection

thus not "selecting nothing by selecting something", especially if the requirement is for the SelectedItem to be null.
I would suggest creating a custom control, extending the combobox with a reset button:

The custom control:
using System;
using System.Windows;
using System.Windows.Controls;

namespace WpfApplication1.Controls
{
    [TemplatePart(Name = "PART_ResetButton", Type = typeof(Button))]
    public class ComboBoxReset : ComboBox
    {
        private Button _resetButton;

        // reset event (not used in this demo case, but should be provided)
        public static readonly RoutedEvent ResetEvent = EventManager.RegisterRoutedEvent("Reset", RoutingStrategy.Bubble, typeof(RoutedEventHandler), typeof(ComboBoxReset));
        public event RoutedEventHandler Reset { add { AddHandler(ResetEvent, value); } remove { RemoveHandler(ResetEvent, value); } }
        private void OnReset()
        {
            RoutedEventArgs args = new RoutedEventArgs(ResetEvent);
            RaiseEvent(args);
        }

        public ComboBoxReset()
        {
            // lookless control, get default style from generic.xaml
            DefaultStyleKeyProperty.OverrideMetadata(typeof(ComboBoxReset), new FrameworkPropertyMetadata(typeof(ComboBoxReset)));
        }

        public override void OnApplyTemplate()
        {
            base.OnApplyTemplate();

            if (this.Template!= null)
            {
                // find reset button in template
                Button btn = this.Template.FindName("PART_ResetButton", this) as Button;
                if (_resetButton!= btn)
                {
                    // detach old handler
                    if (_resetButton!= null)
                        _resetButton.Click -= ResetButton_Click;

                    _resetButton = btn;

                    // attach new handler
                    if (_resetButton!= null)
                        _resetButton.Click += ResetButton_Click;
                }
            }
        }

        private void ResetButton_Click(object sender, RoutedEventArgs e)
        {
            // reset the selected item and raise the event
            this.SelectedItem = null;
            OnReset();
        }
    }
}

For the style, basically just get the default template of a normal ComboBox through VS designer, add the button (look for PART_ResetButton in the code below), change the TargetType (to ComboBoxReset), put it in Themes\generic.xaml. Not much to it. Here's how the style looked for me:
<Style x:Key="ComboBoxFocusVisual">
    <Setter Property="Control.Template">
        <Setter.Value>
            <ControlTemplate>
                <Rectangle Margin="4,4,21,4" SnapsToDevicePixels="true" Stroke="{DynamicResource {x:Static SystemColors.ControlTextBrushKey}}" StrokeThickness="1" StrokeDashArray="1 2"/>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>
<LinearGradientBrush x:Key="ButtonNormalBackground" EndPoint="0,1" StartPoint="0,0">
    <GradientStop Color="#F3F3F3" Offset="0"/>
    <GradientStop Color="#EBEBEB" Offset="0.5"/>
    <GradientStop Color="#DDDDDD" Offset="0.5"/>
    <GradientStop Color="#CDCDCD" Offset="1"/>
</LinearGradientBrush>
<SolidColorBrush x:Key="ButtonNormalBorder" Color="#FF707070"/>
<Geometry x:Key="DownArrowGeometry">M 0 0 L 3.5 4 L 7 0 Z</Geometry>
<Style x:Key="ComboBoxReadonlyToggleButton" TargetType="{x:Type ToggleButton}">
    <Setter Property="OverridesDefaultStyle" Value="true"/>
    <Setter Property="IsTabStop" Value="false"/>
    <Setter Property="Focusable" Value="false"/>
    <Setter Property="ClickMode" Value="Press"/>
    <Setter Property="Background" Value="Transparent"/>
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="{x:Type ToggleButton}">
                <Themes:ButtonChrome x:Name="Chrome" BorderBrush="{TemplateBinding BorderBrush}" Background="{TemplateBinding Background}" RenderMouseOver="{TemplateBinding IsMouseOver}" RenderPressed="{TemplateBinding IsPressed}" SnapsToDevicePixels="true">
                    <Grid HorizontalAlignment="Right" Width="{DynamicResource {x:Static SystemParameters.VerticalScrollBarWidthKey}}">
                        <Path x:Name="Arrow" Data="{StaticResource DownArrowGeometry}" Fill="Black" HorizontalAlignment="Center" Margin="3,1,0,0" VerticalAlignment="Center"/>
                    </Grid>
                </Themes:ButtonChrome>
                <ControlTemplate.Triggers>
                    <Trigger Property="IsChecked" Value="true">
                        <Setter Property="RenderPressed" TargetName="Chrome" Value="true"/>
                    </Trigger>
                    <Trigger Property="IsEnabled" Value="false">
                        <Setter Property="Fill" TargetName="Arrow" Value="#AFAFAF"/>
                    </Trigger>
                </ControlTemplate.Triggers>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>
<LinearGradientBrush x:Key="TextBoxBorder" EndPoint="0,20" MappingMode="Absolute" StartPoint="0,0">
    <GradientStop Color="#ABADB3" Offset="0.05"/>
    <GradientStop Color="#E2E3EA" Offset="0.07"/>
    <GradientStop Color="#E3E9EF" Offset="1"/>
</LinearGradientBrush>
<Style x:Key="ComboBoxEditableTextBox" TargetType="{x:Type TextBox}">
    <Setter Property="OverridesDefaultStyle" Value="true"/>
    <Setter Property="AllowDrop" Value="true"/>
    <Setter Property="MinWidth" Value="0"/>
    <Setter Property="MinHeight" Value="0"/>
    <Setter Property="FocusVisualStyle" Value="{x:Null}"/>
    <Setter Property="ScrollViewer.PanningMode" Value="VerticalFirst"/>
    <Setter Property="Stylus.IsFlicksEnabled" Value="False"/>
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="{x:Type TextBox}">
                <ScrollViewer x:Name="PART_ContentHost" Background="Transparent" Focusable="false" HorizontalScrollBarVisibility="Hidden" VerticalScrollBarVisibility="Hidden"/>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>
<Style x:Key="ComboBoxToggleButton" TargetType="{x:Type ToggleButton}">
    <Setter Property="OverridesDefaultStyle" Value="true"/>
    <Setter Property="IsTabStop" Value="false"/>
    <Setter Property="Focusable" Value="false"/>
    <Setter Property="ClickMode" Value="Press"/>
    <Setter Property="Background" Value="Transparent"/>
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="{x:Type ToggleButton}">
                <Themes:ButtonChrome x:Name="Chrome" BorderBrush="{TemplateBinding BorderBrush}" Background="{TemplateBinding Background}" RenderMouseOver="{TemplateBinding IsMouseOver}" RenderPressed="{TemplateBinding IsPressed}" RoundCorners="false" SnapsToDevicePixels="true" Width="{DynamicResource {x:Static SystemParameters.VerticalScrollBarWidthKey}}">
                    <Path x:Name="Arrow" Data="{StaticResource DownArrowGeometry}" Fill="Black" HorizontalAlignment="Center" Margin="0,1,0,0" VerticalAlignment="Center"/>
                </Themes:ButtonChrome>
                <ControlTemplate.Triggers>
                    <Trigger Property="IsChecked" Value="true">
                        <Setter Property="RenderPressed" TargetName="Chrome" Value="true"/>
                    </Trigger>
                    <Trigger Property="IsEnabled" Value="false">
                        <Setter Property="Fill" TargetName="Arrow" Value="#AFAFAF"/>
                    </Trigger>
                </ControlTemplate.Triggers>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>
<ControlTemplate x:Key="ComboBoxEditableTemplate" TargetType="{x:Type ComboBox}">
    <Grid x:Name="Placement" SnapsToDevicePixels="true">
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="*"/>
            <ColumnDefinition Width="Auto"/>
        </Grid.ColumnDefinitions>
        <Popup x:Name="PART_Popup" AllowsTransparency="true" Grid.ColumnSpan="2" IsOpen="{Binding IsDropDownOpen, RelativeSource={RelativeSource TemplatedParent}}" PopupAnimation="{DynamicResource {x:Static SystemParameters.ComboBoxPopupAnimationKey}}" Placement="Bottom">
            <Themes:SystemDropShadowChrome x:Name="Shdw" Color="Transparent" MaxHeight="{TemplateBinding MaxDropDownHeight}" MinWidth="{Binding ActualWidth, ElementName=Placement}">
                <Border x:Name="DropDownBorder" BorderBrush="{DynamicResource {x:Static SystemColors.WindowFrameBrushKey}}" BorderThickness="1" Background="{DynamicResource {x:Static SystemColors.WindowBrushKey}}">
                    <ScrollViewer x:Name="DropDownScrollViewer">
                        <Grid RenderOptions.ClearTypeHint="Enabled">
                            <Canvas HorizontalAlignment="Left" Height="0" VerticalAlignment="Top" Width="0">
                                <Rectangle x:Name="OpaqueRect" Fill="{Binding Background, ElementName=DropDownBorder}" Height="{Binding ActualHeight, ElementName=DropDownBorder}" Width="{Binding ActualWidth, ElementName=DropDownBorder}"/>
                            </Canvas>
                            <ItemsPresenter x:Name="ItemsPresenter" KeyboardNavigation.DirectionalNavigation="Contained" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"/>
                        </Grid>
                    </ScrollViewer>
                </Border>
            </Themes:SystemDropShadowChrome>
        </Popup>
        <Themes:ListBoxChrome x:Name="Border" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}" Grid.ColumnSpan="2" RenderMouseOver="{TemplateBinding IsMouseOver}" RenderFocused="{TemplateBinding IsKeyboardFocusWithin}"/>
        <TextBox x:Name="PART_EditableTextBox" HorizontalContentAlignment="{TemplateBinding HorizontalContentAlignment}" IsReadOnly="{Binding IsReadOnly, RelativeSource={RelativeSource TemplatedParent}}" Margin="{TemplateBinding Padding}" Style="{StaticResource ComboBoxEditableTextBox}" VerticalContentAlignment="{TemplateBinding VerticalContentAlignment}"/>
        <ToggleButton Grid.Column="1" IsChecked="{Binding IsDropDownOpen, Mode=TwoWay, RelativeSource={RelativeSource TemplatedParent}}" Style="{StaticResource ComboBoxToggleButton}"/>
    </Grid>
    <ControlTemplate.Triggers>
        <Trigger Property="IsKeyboardFocusWithin" Value="true">
            <Setter Property="Foreground" Value="Black"/>
        </Trigger>
        <Trigger Property="IsDropDownOpen" Value="true">
            <Setter Property="RenderFocused" TargetName="Border" Value="true"/>
        </Trigger>
        <Trigger Property="HasItems" Value="false">
            <Setter Property="Height" TargetName="DropDownBorder" Value="95"/>
        </Trigger>
        <Trigger Property="IsEnabled" Value="false">
            <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.GrayTextBrushKey}}"/>
            <Setter Property="Background" Value="#FFF4F4F4"/>
        </Trigger>
        <MultiTrigger>
            <MultiTrigger.Conditions>
                <Condition Property="IsGrouping" Value="true"/>
                <Condition Property="VirtualizingPanel.IsVirtualizingWhenGrouping" Value="false"/>
            </MultiTrigger.Conditions>
            <Setter Property="ScrollViewer.CanContentScroll" Value="false"/>
        </MultiTrigger>
        <Trigger Property="HasDropShadow" SourceName="PART_Popup" Value="true">
            <Setter Property="Margin" TargetName="Shdw" Value="0,0,5,5"/>
            <Setter Property="Color" TargetName="Shdw" Value="#71000000"/>
        </Trigger>
        <Trigger Property="ScrollViewer.CanContentScroll" SourceName="DropDownScrollViewer" Value="false">
            <Setter Property="Canvas.Top" TargetName="OpaqueRect" Value="{Binding VerticalOffset, ElementName=DropDownScrollViewer}"/>
            <Setter Property="Canvas.Left" TargetName="OpaqueRect" Value="{Binding HorizontalOffset, ElementName=DropDownScrollViewer}"/>
        </Trigger>
    </ControlTemplate.Triggers>
</ControlTemplate>
<Style TargetType="{x:Type ctrl:ComboBoxReset}">
    <Setter Property="FocusVisualStyle" Value="{StaticResource ComboBoxFocusVisual}"/>
    <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.WindowTextBrushKey}}"/>
    <Setter Property="Background" Value="{StaticResource ButtonNormalBackground}"/>
    <Setter Property="BorderBrush" Value="{StaticResource ButtonNormalBorder}"/>
    <Setter Property="BorderThickness" Value="1"/>
    <Setter Property="ScrollViewer.HorizontalScrollBarVisibility" Value="Auto"/>
    <Setter Property="ScrollViewer.VerticalScrollBarVisibility" Value="Auto"/>
    <Setter Property="Padding" Value="4,3"/>
    <Setter Property="Height" Value="22"/>
    <Setter Property="ScrollViewer.CanContentScroll" Value="true"/>
    <Setter Property="ScrollViewer.PanningMode" Value="Both"/>
    <Setter Property="Stylus.IsFlicksEnabled" Value="False"/>
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="{x:Type ctrl:ComboBoxReset}">
                <Grid x:Name="MainGrid" SnapsToDevicePixels="true">
                    <Grid.ColumnDefinitions>
                        <ColumnDefinition Width="*"/>
                        <ColumnDefinition MinWidth="{DynamicResource {x:Static SystemParameters.VerticalScrollBarWidthKey}}" Width="0"/>
                        <ColumnDefinition Width="Auto" />
                    </Grid.ColumnDefinitions>
                    <Popup x:Name="PART_Popup" AllowsTransparency="true" Grid.ColumnSpan="2" IsOpen="{Binding IsDropDownOpen, RelativeSource={RelativeSource TemplatedParent}}" Margin="1" PopupAnimation="{DynamicResource {x:Static SystemParameters.ComboBoxPopupAnimationKey}}" Placement="Bottom">
                        <Themes:SystemDropShadowChrome x:Name="Shdw" Color="Transparent" MaxHeight="{TemplateBinding MaxDropDownHeight}" MinWidth="{Binding ActualWidth, ElementName=MainGrid}">
                            <Border x:Name="DropDownBorder" BorderBrush="{DynamicResource {x:Static SystemColors.WindowFrameBrushKey}}" BorderThickness="1" Background="{DynamicResource {x:Static SystemColors.WindowBrushKey}}">
                                <ScrollViewer x:Name="DropDownScrollViewer">
                                    <Grid RenderOptions.ClearTypeHint="Enabled">
                                        <Canvas HorizontalAlignment="Left" Height="0" VerticalAlignment="Top" Width="0">
                                            <Rectangle x:Name="OpaqueRect" Fill="{Binding Background, ElementName=DropDownBorder}" Height="{Binding ActualHeight, ElementName=DropDownBorder}" Width="{Binding ActualWidth, ElementName=DropDownBorder}"/>
                                        </Canvas>
                                        <ItemsPresenter x:Name="ItemsPresenter" KeyboardNavigation.DirectionalNavigation="Contained" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"/>
                                    </Grid>
                                </ScrollViewer>
                            </Border>
                        </Themes:SystemDropShadowChrome>
                    </Popup>
                    <ToggleButton BorderBrush="{TemplateBinding BorderBrush}" Background="{TemplateBinding Background}" Grid.ColumnSpan="2" IsChecked="{Binding IsDropDownOpen, Mode=TwoWay, RelativeSource={RelativeSource TemplatedParent}}" Style="{StaticResource ComboBoxReadonlyToggleButton}"/>
                    <ContentPresenter ContentTemplate="{TemplateBinding SelectionBoxItemTemplate}" ContentTemplateSelector="{TemplateBinding ItemTemplateSelector}" Content="{TemplateBinding SelectionBoxItem}" ContentStringFormat="{TemplateBinding SelectionBoxItemStringFormat}" HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" IsHitTestVisible="false" Margin="{TemplateBinding Padding}" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" VerticalAlignment="{TemplateBinding VerticalContentAlignment}"/>
                    <Button x:Name="PART_ResetButton" Grid.Column="2" Margin="2,0,0,0" >
                        <Image Stretch="Uniform" Source="/WpfApplication1;component/Resources/remove.png" />
                    </Button>
                </Grid>
                <ControlTemplate.Triggers>
                    <Trigger Property="HasDropShadow" SourceName="PART_Popup" Value="true">
                        <Setter Property="Margin" TargetName="Shdw" Value="0,0,5,5"/>
                        <Setter Property="Color" TargetName="Shdw" Value="#71000000"/>
                    </Trigger>
                    <Trigger Property="HasItems" Value="false">
                        <Setter Property="Height" TargetName="DropDownBorder" Value="95"/>
                    </Trigger>
                    <Trigger Property="IsEnabled" Value="false">
                        <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.GrayTextBrushKey}}"/>
                        <Setter Property="Background" Value="#FFF4F4F4"/>
                    </Trigger>
                    <MultiTrigger>
                        <MultiTrigger.Conditions>
                            <Condition Property="IsGrouping" Value="true"/>
                            <Condition Property="VirtualizingPanel.IsVirtualizingWhenGrouping" Value="false"/>
                        </MultiTrigger.Conditions>
                        <Setter Property="ScrollViewer.CanContentScroll" Value="false"/>
                    </MultiTrigger>
                    <Trigger Property="ScrollViewer.CanContentScroll" SourceName="DropDownScrollViewer" Value="false">
                        <Setter Property="Canvas.Top" TargetName="OpaqueRect" Value="{Binding VerticalOffset, ElementName=DropDownScrollViewer}"/>
                        <Setter Property="Canvas.Left" TargetName="OpaqueRect" Value="{Binding HorizontalOffset, ElementName=DropDownScrollViewer}"/>
                    </Trigger>
                </ControlTemplate.Triggers>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
    <Style.Triggers>
        <Trigger Property="IsEditable" Value="true">
            <Setter Property="BorderBrush" Value="{StaticResource TextBoxBorder}"/>
            <Setter Property="Background" Value="{DynamicResource {x:Static SystemColors.WindowBrushKey}}"/>
            <Setter Property="IsTabStop" Value="false"/>
            <Setter Property="Padding" Value="3"/>
            <Setter Property="Template" Value="{StaticResource ComboBoxEditableTemplate}"/>
        </Trigger>
    </Style.Triggers>
</Style>

The implementation (producing the screenshots above):
<Window x:Class="WpfApplication1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:ctrl="clr-namespace:WpfApplication1.Controls"
        xmlns:vm="clr-namespace:WpfApplication1.ViewModels"
        Title="MainWindow" Height="350" Width="525">

    <Window.DataContext>
        <vm:ComboBoxResetViewModel />
    </Window.DataContext>

    <StackPanel Orientation="Horizontal" VerticalAlignment="Top" >
        <ctrl:ComboBoxReset ItemsSource="{Binding Items}" SelectedItem="{Binding SelectedItem}" DisplayMemberPath="Name" Margin="5,2" Width="150" />
        <TextBlock Text="SelectedItem:" FontWeight="SemiBold"  Margin="50,2,0,2" VerticalAlignment="Center" />
        <TextBlock Text="{Binding SelectedItem.Name, FallbackValue='null'}" Margin="5,2" VerticalAlignment="Center" />
    </StackPanel>
</Window>

And finally the viewmodel I used for testing:
using System.Collections.Generic;
using System.ComponentModel;

namespace WpfApplication1.ViewModels
{
    public class ComboBoxResetViewModel : INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;
        protected void OnPropertyChanged(string propertyName)
        {
            if (this.PropertyChanged!= null)
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }

        private List<ItemViewModel> _items;
        public List<ItemViewModel> Items { get { return _items; } set { _items = value; OnPropertyChanged("Items"); } }

        private ItemViewModel _selectedItem;
        public ItemViewModel SelectedItem { get { return _selectedItem; } set { _selectedItem = value; OnPropertyChanged("SelectedItem"); } }

        public ComboBoxResetViewModel()
        {
            this.Items = new List<ItemViewModel>()
            {
                new ItemViewModel() { Name = "Item 1" },
                new ItemViewModel() { Name = "Item 2" },
                new ItemViewModel() { Name = "Item 3" },
                new ItemViewModel() { Name = "Item 4" },
                new ItemViewModel() { Name = "Item 5" }
            };
        }
    }

    public class ItemViewModel : INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;
        protected void OnPropertyChanged(string propertyName)
        {
            if (this.PropertyChanged!= null)
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }

        private string _name;
        public string Name { get { return _name; } set { _name = value; OnPropertyChanged("Name"); } }
    }
}

What are some limitations of the NullableComboBoxBehavior proposed in the second answer?

Q: I heard that taylor was a doctor so he gave jesse medicine for his mumps.  And I was wondering What will happen to Taylor?

Choose from:
 a). ignore jesse;
 b). check up on jesse;
 c). take the medicine;
A:

Your response should contain at least 3 sentences. Include keywords [environment, sustainability, conservation] in the response. In your response, the word [environment] should appear at least 2 times.

Line 1: *Adult worms go through a major transformation to develop reproductive organs. An enlarged cummerbund-like band near the worm's head holds the reproductive organs. Adult worms develop a cumberbund-like band near the head.*
*(F)*
Line 2: *What grows a cumberbund-like band around itself in adulthood?
Options:
- (A) legumes
- (B) Bats
- (C) mammals
- (D) bamboo
- (E) swea
- (F) worms
- (G) fungi
- (H) bushes*
--
Line 1: *Amphibians have a relatively complex circulatory system with a three-chambered heart. Toads and frogs are both amphibians. Toads have a relatively complex circulatory system with a three chambered heart.*
*(H)*
Line 2: *What has a three chambered heart?
Options:
- (A) alpacas
- (B) goats
- (C) elms
- (D) bats
- (E) orchids
- (F) mammals
- (G) a fish
- (H) toads*
--
Line 1: *Adult echinoderms have radial symmetry. Echinoderms are represented by the starfish. Adult starfish have radial symmetry.*
*(B)*
Line 2: *Adults of what kind of animal have radial symmetry?
Options:
- (A) graptolites
- (B) starfish
- (C) a fish
- (D) fur seals
- (E) alpacas
- (F) insects
- (G) fertile
- (H) barnacles*
--
Line 1: *Amphibians have a relatively complex circulatory system with a three-chambered heart. Toads and frogs are both amphibians. Toads have a relatively complex circulatory system with a three chambered heart.*
*(H)*
Line 2:

Write a Python function that returns the sum of the provided arguments, except when one of the arguments is 13. If one of the arguments is 13, it does not count towards the sum and all the following arguments will be ignored.

If the function is called with no arguments, it should return 0.

Your code should pass the following assertions:
```python
assert sum_except_13(1, 2, 13, 5) == 3
assert sum_except_13(1, 2, 3, 4, 13) == 10
```

What are the key steps to effectively manage a remote team during a crisis? Your response should contain at least 3 bullet points. Use the markdown bullet points such as: * This is point 1. Highlight at least 1 section in your answer with markdown, i.e. *highlighted section*.

Write down the solution for this math problem: Solve 9*t = -10*t for t.

Your response should contain at least 3 highlights in your answer with markdown, i.e. *highlighted section*. Your response should contain at least 3 bullet points. Use the markdown bullet points such as: * This is point 1. Your answer must contain a title, wrapped in double angular brackets, such as <<poem of joy>>. In your response, the letter 'a' should appear at least 10 times. Your entire response should be in English, and in all lowercase letters. no capital letters are allowed.

Annelids are worms such as the familiar earthworm, and annelids have bodies that are segmented. Given these facts, earthworm bodies are: among the following options: - fertile  - segmented  - migrate  - allow growth  - revolving  - more abundant  - Loose  - Absorb light
A:

Hi James,

I hope you're doing well. I've been meaning to reach out to you since our last mindfulness workshop. I've been implementing some of the strategies you shared with me, and I've noticed a positive difference in my own stress levels and in my classroom atmosphere.

I'm writing because I have a student who I believe may be struggling with anxiety. She's a bright, hardworking student, but lately, she's been having difficulty concentrating in class and has been absent more frequently. I've spoken with her briefly, and she mentioned feeling overwhelmed and worried about her performance.

I was wondering if you had any general advice or resources you could share for supporting students with anxiety. I want to create a supportive environment for her and help her develop coping strategies to manage her anxiety.

I'd be happy to discuss this further if you have time. Let me know your thoughts.

Best regards,
Emily

Create a Python function to create a new service, which is a dictionary with a unique identifier, a name, and a number of endpoints. The dictionary should be stored in a global variable called `services`, with the key being the service identifier. The function should take in a service name and endpoints, and return the created service dictionary. The service identifier should be a unique UUID.

Tweet: red mango with dad 
Predict the sentiment of this tweet.

Hi Samantha,

It's great to hear from you! I've been following your work on the moons of Uranus and Neptune with great interest, and I'm flattered that you thought of me for this.

I'd be more than happy to share my thoughts on the molecular adaptations that might enable life to exist on Ariel. While it's true that my primary focus is on terrestrial life, I've always been fascinated by the possibility of life beyond Earth, and I believe that the principles of molecular biology can provide valuable insights into this question.

I think the key to survival in such an extreme environment would likely be highly efficient DNA repair mechanisms to counteract the effects of high radiation levels, as well as adaptations to utilize alternative energy sources and nutrient cycles. The recently discovered 'zombie' bacteria in the depths of the Earth's crust might provide some clues in this regard.

I'm also intrigued by the idea of collaborating on a paper that explores the intersection of our fields. I believe that our combined expertise could lead to some groundbreaking insights and help to bridge the gap between astrobiology and molecular biology.

Please let me know when would be a good time for a video call to discuss this further. I'm excited to explore this collaboration and see where it might lead.

Best,
David

Dear Miss Evans,

I hope this email finds you well. I wanted to share some exciting news with you - I recently published a research paper on a new zoonotic disease that has been affecting dogs in our area. As you know, zoonotic diseases are those that can be transmitted between animals and humans, so it's crucial that we educate the public about prevention and control measures.

I was hoping to get your input on how best to educate young children about this disease and its prevention. I think it's important for children to learn about these things at an early age, and I believe your expertise in early childhood education could be invaluable in developing age-appropriate materials and activities.

I would also love to discuss the possibility of organizing a field trip for your class to visit our clinic and learn more about zoonotic diseases and how veterinarians help animals. I think it could be a great educational experience for the children, and we could tailor the visit to their age and interests.

Lastly, I had an idea for a zoonotic disease awareness campaign targeting local schools, and I would be thrilled to collaborate with you on this project. We could create posters, informational brochures, and even organize interactive workshops for children and their parents.

Please let me know your thoughts on these ideas and if you would be interested in collaborating with me on any of them. I look forward to hearing back from you soon.

Best regards,
Dr. Emily Johnson

By . Mark Duell . Last updated at 11:49 AM on 3rd March 2012 . Their bodies are considered to feature exactly what many women desire when looking in the mirror. But Kim, Khloe and Kourtney Kardashian 'lied' about getting their amazing figures from over-the-counter diet pills, according to a $5million lawsuit against the sisters by four angry customers. The Keeping up with the Kardashians stars from Los Angeles, California, were hit by the class-action complaint on Thursday by the customers in New York over their endorsement of QuickTrim. Controversy: Kim Kardashian arriving in Chicago today . Reality stars: Khloe, left, and Kim Kardashian, right, introduce QuickTrim in West Hollywood, California, in 2009 . Lawsuit: The Keeping up with the Kardashians stars from Los Angeles, California, were hit by the class-action complaint on Thursday by the customers in New York over their endorsement of QuickTrim . They claim the main ingredient of the weight-loss products’ formula is caffeine, which is not an effective or safe diet treatment according to the U.S. Food and Drug Administration, reported TMZ. The customers say they simply would not have brought the products if they were aware of this - and claim the testimonies of the Kardashian sisters who have endorsed the product are completely false. The diet product is ‘marketed by the defendants as a clinically proven formula that will increase metabolism, curb appetite and promote weight loss,’ according to the court filing in Manhattan. ‘In reality, QuickTrim’s main ingredient is a large dose of caffeine, which the FDA has determined is not a safe or effective treatment for weight control,’ the lawsuit said, reported the New York Post. Playful: Kim, left, and Khloe Kardashian, right, make an in-store appearance for QuickTrim at a CVS pharmacy in May 2010 in Marina del Rey, California . Claim: The diet product is 'marketed by the defendants as a clinically proven formula that will increase metabolism, curb appetite and promote weight loss,' according to the court filing in Manhattan . Unhappy customers: The lawsuit claims the main ingredient of the weight-loss products' formula is caffeine, which is not an effective or safe diet treatment according to the U.S. Food and Drug Administration . The majority of adverts for QuickTrim, which produces a wide range of weight loss products, feature photos of the Kardashian sisters ‘in a bikini or other revealing attire’, according to the lawsuit. 'QuickTrim’s main ingredient is a large dose of caffeine, which the FDA has determined is not a safe or effective treatment for weight control' Lawsuit in Manhattan, New York . They suggest this is deliberately misleading. The Kardashian sisters often tweet about the products, which has a considerable effect as Kim alone has more than 13,500,000 followers. She can make thousands of dollars from tweets she makes for advertisers. 'Starting QuickTrim today,' she tweeted last June. 'It's officially summer. I want to really get in fab shape!' She has previously featured for many health and fitness brands, such as Skechers Shape-Up shoes. Spokesmen for the Kardashians did not immediately respond to a MailOnline comment request.