单项选择题

在窗体上画一个命令按钮，然后编写如下程序：
Sub S1(By Val x As Integer, By Val y As Integer)
Dim t As Integer
t=x
x=y
y=r
End Sub
Private Sub Command1_Click()
Dim a As Integer, b As Integer
a=10
b=30
S1 a，b
Print"a=";"b=";b
End Sub
程序运行后，单击命令按钮,．输出结果是______。

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