You use Microsoft .NET Framework 4 to create a Windows Presentation Foundation (WPF) application. 
You need to ensure that users can view content in a book-reading format that displays two pages at a time. 
Which control should you use?（）

You use Microsoft .NET Framework 4 to create a Windows Forms application.
You write the following code segment. (Line numbers are included for reference only.)

You need to ensure that the first time each user opens the application, a text field displays the following message: "Please enter your setting."
Which code segment should you insert at line 03? （）