下面程序： Private Sub Form_Click() Dim x，y，z As Integer x=5 Y=7 z=0 Call P1(x,y,z) Print Str(z) End Sub Sub P1(ByVal a As Integer, ByVal b As Integer, c As Integer) c=a+b End Sub 运行后的输出结果为______。

A．0

B．12

C．Str(

D．显示错误信息