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?（）

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?（）