C++语言中标点符号中表示一条预处理命令开始的是（ ）。

A．Private Sub Form_Mouse Down(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，Shin As Integer，-　　　　　　　X As Single，Y As Single)　　　　If(Button=vbLeftButton)Or(Button=vbRightButton)Then PopupMenu Bs　　End Sub

A．15
B．16
C．17
D．18