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______。