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 ______。

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