单选题 编写如下事件过程：
Private Sub Form_ MouseDown (Button As Integer, _
Shift As Integer, X As Single, Y As Single)
If Shift = 6 And Button = 2 Then
Print "BBBB"
End If
End Sub
程序运行后，为了在窗体上输出BBBB，应执行的操作为______ 。