You use Microsoft Visual Studio 2010 and Microsoft .NET Framework 4 to create a Windows Presentation Foundation (WPF) application. You write the following code fragment. You need to ensure that the StringMember property of the data-bound object is updated immediately when the user types the TextBox control. Which binding expression should you use?（）

• A、 { Binding Path=StringMember, Mode=TwoWay }
• B、 { Binding Path=StringMember, NotifyOnSourceUpdated=True }
• C、 { Binding Path=StringMember, NotifyOnTargetUpdated=True }
• D、 { Binding Path=StringMember, UpdateSourceTrigger=PropertyChanged }