You use Microsoft .NET Framework 4 to create a Windows Presentation Foundation (WPF) application. You write the following code segment. The TextBox control is data-bound to an instance of the Contact class. You plan to implement an ErrorTemplate in the TextBox control. You need to ensure that the validation error message is displayed next to the TextBox control. Which code fragment should you use?（）

• A、
• B、
• C、
• D、