单项选择题 You use Microsoft .NET Framework 4 to create a Windows Presentation Foundation (WPF) application. You want the application to contain a window as shown in the following exhibit. The application contains the following code fragment. (Line numbers are included for reference only.) You need to create the application window. Which code fragment should you insert at line 12?（）

单项选择题 You use Microsoft .NET Framework 4 to create a Windows Presentation Foundation (WPF) application. You plan to create a window that has a layout as shown in the following exhibit. You need to define the code fragment to create the window layout. You also need to ensure that the window contains a splitter line. Which code fragment should you use?（）

单项选择题 You use Microsoft .NET Framework 4 to create a Windows Presentation Foundation (WPF) application. The application contains a window as shown in the following exhibit. You need to define a DockPanel control that fits the window. Which code fragment should you use? （）