单选题 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______。