执行下列程序后，鼠标单击窗体，输出结果为 Private Sub Form_Click() Print "Click"； End Sub Private Sub Form_MouseDown(Button As Integer，Shift As Integer，X As Single，Y As Single) Print "Donw" End Sub Private Sub Form_MouseUp(ButtonAs Integer，Shift As Integer，X As Single，Y As Single) Print "Up" End Sub

A．All Files(*.*)
B．Text Files(*.*)
C．*.txt
D．All Files(*.*)|Text Files(*.*)

设已经在菜单编辑器中设计了窗体的快捷菜单，某顶级菜单为a1，且取消其“可见”属性。运行时，哪个事件过程可以使快捷菜单的菜单项响应鼠标左键单击和右健单击的事件过程是 Ａ) Private Sub Form_MouseDown(Button As Integer，Shift As Integer，X As Single，Y As Single) If Button=2 Then PopupMenu a1，2 End Sub Ｂ) Private Sub Form_MouseDown(ButtonAsInteger，ShiftAsInteger，X As Single，Y As Single) PopupMenu a1，0 End Sub Ｃ) Private Sub Form_Mouse Down(Button As Integer，Shift As Integer，X As Single，Y As Single) PopupMenu a1 End Sub Ｄ) Private Sub Form_MouseDown(Button As Integer，Shift As Integer，X As Single，Y As Single) If(Button=vbLetfButton) Or (Button=vbRightButton) Then PopupMenu a1 End Sub