选择题 16.  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(By Val a As Integer, By Val b As Integer, c As Integer)
    c=a+b
    End Sub
    运行后的输出结果为______。