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? （）

You use Microsoft .NET Framework 4 to create a Windows Presentation Foundation (WPF) application. 
You create a game where a ball drops from the top to the bottom of a window.
You plan to create a single animation for the game.
You need to ensure that the animation shows the ball bounce.
What should you do?（）