假定已经在菜单编辑器中建立了窗体的弹出式菜单,其顶级菜单的名称为a1,其“可见”属性为False,则程序运行后,可以同时响应鼠标左键单击和右键单击的事件过程是 ______ 。
A.Private Sub Form_ MouseDown (Button As Integer, _ Shift As Integer, X As Single, Y As Singl If Button = 1 And Button = 2 ThenPopupMenu al End If End Sub B.Private Sub Form_ MouseDown (Button As Integer, _ Shift As Integer, X As Single, Y As SinglPopupMenu a1 End Sub C.Private Sub Form_ MouseDown (Button As Integer, _ Shift As Integer, X As Single, Y As SinglIf Button = 1 Then PopupMenu a 1End If End Sub D.Private Sub Form_ MouseDown(Button As Integer, _ Shift As Integer, X As Single, Y As SinglIf Button = 2 Then PopupMenu a 1End If End Sub