敬求!would should 在虚拟语气中有什么区别,还有could.特别是后面跟have down的时候,在选择..

could have done本来能够做什么,事实上没做
should have done本应该做某事却没有做,表示责备和遗憾.
would have done将来可能做
如; You should have told me the news eariler.
would 表示与事实相反.
1.If I were a bird,I would be happy.(与现在事实相反)
2.If I had told him the news,he would have cried..(与过去事实相反)
3.If I were to go tomorrow,I would take a plane..(与将来事实相反)

would/should/could/might都可以跟have down, 都是表示对过去发生动作的一种虚拟，四个词只是在意思上有所不同。would表示：就会 should表示：本应该 could表示：就能怎样 might表示就可能怎样。例句：
1. If I had come the day before, I would have met him. 如果我前一天来的话，我就...

在虚拟语气中，这几个情态动词其实没有多大的区别的哦。
表示与过去事实相反的情况下，从句用had done，主句用would have done，你只要记住这个就可以了。一般选择题都是挖空半句，然后让你根据题目填出正确的形式的。