问题描述：
It is a pity that you should have to leave.这句话中为什么要用should have to do?
should的虚拟语气或者说“本应该做而没有做”是should have done，但这里的should have to do怎么解释？
should的虚拟语气或者说“本应该做而没有做”是should have done，但这里的should have to do怎么解释？
问题解答：
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