Which XAML fragment should you insert at lines 03 and 04?

You are developing a Silverlight 4 application.
You have a page that contains the following XAML fragment.
<StackPanel Orientation=”Vertical”>
<Grid x:Name=”Master”>
<ListBox x:Name=”lstOrders” />
</Grid>
<Grid x:Name=”Details”>
<ListBox x:Name=”lstOrdersDetails” />
<myControls:DetailsViewLoading />
</Grid>
</StackPanel>
The application defines the DetailsViewLoading user control by using the following XAML fragm ent. (Line numbers are included for reference only.)

01 <UserControl x:Class=”DetailsViewLoading” xmlns=http://schemas.microsoft.com/winfx/2006/xaml/presentation xmlns:x=”http://schemas.microsoft.com/winfx/2006/xaml”>
02 <Grid>
03
04
05 <StackPanel>
06 <TextBlock Text=”Loading Details…”/>
07 <Button Content=”Close” Click=”CloseBtn_Click”/>
08 </StackPanel>
09 </Border>
10 </Grid>
11 </UserControl>

You need to display the DetailsViewLoading user control on top of the other content in the Details Grid control. You also need to ensure that the rest of the content in the Details Grid control is unavailable until the DetailsViewLoading user control is closed. Which XAML fragment should you insert at lines 03 and 04?

A.
<Border CornerRadius=”30″ Background=”#FF5C7590″ Width=”600″ Height=”250″>
<Rectangle HorizontalAlignment=”Stretch” VerticalAlignment=”Stretch” Opacity=”0.765″ Fill=”#FF8A8A8A”/>

B.
<Rectangle HorizontalAlignment=”Stretch” VerticalAlignment=”Stretch” Opacity=”0.765″ Fill=”#FF8A8A8A”/>
<Border CornerRadius=”30″ Background=”#FF5C7590″ Width=”600″ Height=”250″>

C.
<Border CornerRadius=”30″ Background=”#FF5C7590″ Width=”600″ Height=”250″>
<Rectangle HorizontalAlignment=”Center” VerticalAlignment=”Center” Opacity=”0.765″ Fill=”#FF8A8A8A”/>

D.
<Rectangle HorizontalAlignment=”Center” VerticalAlignment=”Center” Opacity=”0.765″ Fill=”#FF8A8A8A”/>
<Border CornerRadius=”30″ Background=”#FF5C7590″ Width=”600″ Height=”250″>