与过去事实相反的非真实条件句啊，从句用过去完成时，主句中用would/could/should/+have done比如说 if you had done your homework,you would not have been criticized by him
should have done 是本应该做什么
你说的应该是虚拟语气的条件状语从句，第二种情况应该是发生在主句中，一般是与过去事实相反从句用第一种形式，主句用第二种形式
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