选择题   若有以下两个过程：
    Sub S1 (ByVal x As Integer, ByVal y As Integer)
    im t As Integer
    t = x
    x = y
    y = t
    End Sub
    Sub S2(x As Integer, y As Integer)
    Dim t As Integer
    t = x : x = y : y = t
    End Sub
    则下列说法中，正确的是______。