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單項(xiàng)選擇題

You use Microsoft .NET Framework 4 to create a Windows Presentation Foundation (WPF) application. 
You write the following code fragment.

You need to ensure that the ButtonHandler method is not executed when the user clicks the CancelButton button. 
Which code segment should you add to the code-behind file?()
 

A.
B.
C.
D.

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