You use Microsoft .NET Framework 4 to create a Windows Presentation Framework (WPF) application.  
You plan to create a custom control that contains four text input fields.
Each of the text input fields within the control will contain a label. 
You need to ensure that the text input fields within the control can be validated by using a regular expression validator. 
Which class should you inherit from?（）

You use Microsoft .NET Framework 4 to create a Windows Presentation Foundation (WPF) application. 
You add a custom command as a resource. The key of the command is saveCommand. 
You write the following code fragment. (Line numbers are included for reference only.) 

You need to ensure that saveCommand is executed when the user clicks the Button control.
What should you do? （）