单击命令按钮时，下列程序的执行结果为　　Private Sub Command1_Click()　　　Dim a As Integer，b As Integer，c As Integer　　　a=2：b=3：C=4
　　　Print P2(c，b，

A．

　　End Sub

　　Private Function P1(x As Integer，y As Integer，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(z，x，y) + X

　　End Function
A) 21
B．19
C．17
D．34