单项选择题 You use Microsoft .NET Framework 4 to create a Windows Presentation Foundation (WPF) application. The application contains three text boxes named txtAddress, txtCity, and txtState. You need to ensure that the postal code is automatically set based on the information typed by users in the text boxes. You also need to ensure that the complete address is displayed in a TextBlock control. Which code fragment should you use?（）

单项选择题 You use Microsoft .NET Framework 4 to create a Windows Forms application. You have a DataGridView that is bound to a DataTable containing a column named ProductName. The ProductName column can contain any valid string, except "ProductX," "ProductY," "ProductZ." You need to ensure that only valid entries for ProductName are saved when users edit the DataGridView. Which DataGridView event should you use?（）

单项选择题 You use Microsoft .NET Framework 4 to create a Windows Presentation Foundation (WPF) application. You add a DataGrid named gridContacts that is data-bound to a collection of Contacts. Each item has the ContactName and Phone properties. The DataGrid contains a column named ContactNameColumn that is bound to ContactName. You write the following code fragment. You need to ensure that the application meets the following requirements: Phone number is shown as a row detail when the row is selected. Only ContactName can be edited. What should you do?（）