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)