问题详情

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al，其“可见”属性为False。程序运行后，单击鼠标左键或右键都能弹出菜单的事件过程是()。
A.Private Sub Form_MouseDown(Button As Integer，_Shift As Integer，X As Single， Y As Single) If Button=1 And Blltton=2Then PopupMenu a1 End If End Sub
B.Private Stlb Form_MouseDown(Button As Integer，_Shift As Integer，X As Single， Y As Single) PopupMenu a1 End Sub
C.Private Sub Form—MouseDown(Button As Integer，_Shift As Integer，X As Single， Y As Single) If Button=1 Then PopupMenu a1 End If End Sub
D.Private Sub Form. MouseDown(Button As Integer，_Shift As Integer，X As Single， Y As Single) If Buttcn=2 Then PopupMenu a1 End If End Sub请帮忙给出正确答案和分析，谢谢！