在FDDI帧结构当中包括前导码、帧首定界符、（）、目的地址、源地址等共计9个字段。

以下程序运行后，单击命令按钮，窗体显示的结果是 ______。 Private Function p1(x As Integer，y As Integel，z As Integer)p1=2*x+y+3*z End Function Private Function p2(x As Integer，y As Integer，z As Integer)p2=p1(2，y，x)+x End Function Private SubCommandl_Click()Dim a As IntegerDim b As IntegerDim c As Integera=2:b=3:c=4Print p2(c，b，A) End Sub

A．19

B．21

C．22

D．23