Excel三個下拉互斥

描述：Excel有三個下拉列表，若選擇了其中任意一個下拉，其他兩個均不可以在選擇。

嘗試了很多種辦法，級聯，數據有效性等等，最後都沒實現。

老大，最後用VBA實現。

附上代碼：

Private Sub Worksheet_Change(ByVal Target As Range)
    Dim r As Long
    Dim n As Integer
    n = 1
    If Target.Column = 2 And Target.Value <> "" Then
        r = Target.Row
        If Range("G" & r).Value <> "" Then
            MsgBox (" G 列已有內容")
            Target = ""
            Exit Sub
        ElseIf Range("I" & r).Value <> "" Then
            Target = ""
            MsgBox (" I 列已有內容")
            Exit Sub
        End If
    End If

    If Target.Column = 7 And Target.Value <> "" Then
        r = Target.Row
        If Range("B" & r).Value <> "" Then
            Target = ""
            MsgBox (" B 列已有內容")
            Exit Sub
        ElseIf Range("I" & r).Value <> "" Then
            Target = ""
            MsgBox (" I 列已有內容")
            Exit Sub
        End If
    End If

    If Target.Column = 9 And Target.Value <> "" Then
        r = Target.Row
        If Range("G" & r).Value <> "" Then
            Target = ""
            MsgBox (" G 列已有內容")
            Exit Sub
        ElseIf Range("B" & r).Value <> "" Then
            Target = ""
            MsgBox (" B 列已有內容")
            Exit Sub
        End If
    End If

End Sub