设已经在“菜单编辑器”中设计了窗体的快捷菜单，其顶级菜单为Bs，取消其“可见”属性，运行时，在以下事件过程中，可以使快捷菜单响应鼠标右键的是( )
A．Private Sub Form_MouseDown(Button As Integer，Shift As Integer，X As Single，Y As Single)
If Button=2 Then PopupMenu Bs,2
End Sub
B．Private Sub Form_MouseDown(Button As Integer，Shift As Integer，X As Single，Y As Single)
PopupMenu Bs
End Sub
C．Private Sub Form—MouseDown(Button As Integer，Shift As Integer，X As Single，Y As Single)
PopupMenu Bs,0
End Sub
D．Private Sub Form_MouseDown(Button As Integer,Shift As Integer,X As Single,Y As Single)
If(Button=vbLeftButton)0r(Button=vbRightButton)Then PopupMenu Bs
End Sub
参考答案：A
解析： PopupMenu方法用来显示弹出式菜单，其格式为：[对象.]PopupMenu菜单名[,Flags][,X,Y,][Bold-Command]。其中，[,Flags][,X,Y,]用来设置菜单的显示位置。为了显示菜单，通常把PopupMenu方法放到MouseDown事件中，按照惯例，一般通过单击鼠标右键显示菜单，这可以用Button参数来实现，鼠标右键的参数为2，因此选项A正确。