You use Microsoft .NET Framework 4 to create a Windows Presentation Foundation (WPF) application. 
The application contains a set of Button controls. 
You need to ensure that a button is highlighted when the mouse pointer is located over a button that contains no content. 
Which code fragment should you use?（）

You use Microsoft .NET Framework 4 to create a Windows Presentation Foundation (WPF) application. 
You create a Button control for the application. 
You need to ensure that the application meets the following requirements: 
When the mouse pointer is over the Button control, the background color of the button is set to red and the Button control appears bigger. 
When the mouse pointer is not over the Button control, the button returns to its original state. 
What should you do?（）