单项选择题

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(z)
D.显示错误信息