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(Button As Integer，Shift As Integer，X As Single，Y As single)
Print "Up"
End Sub

A．Open"c:\student.dat"For Input As # 1 len=len(student)
B．Open"c:\student.dat:For random As # 1 len=len(student)
C．Open"c:\student.dat"For Output As # 1 len=len(student)
D．Open"c:\student.dat"For Append As # 1 len=len(student)

A．12
B．13
C．14
D．15