Question

必修三英语语法，should have done ,could have done,might,m

必修三英语语法，should have done ,could have done,might,must,needn't等等之类的，什么'过去本应该做的却没做之类的…，觉得好乱，好多，很难记忆，在选择题中总选错，希望英语好的帮我解析下，如何用，区分等，谢谢！

Answer 1

should have done只用于谈论过去情况，主要有两个用法：
用于推测过去已经发生的情况。如：
　　He should have arrived by now. 此时他本该到了。
用于指本该发生而实际上未发生的情况。如
Look at the time！ We should have been at the theatre ten minutes ago. 瞧都什么时候了！ 十分钟前我们就该到戏院了。

could have done
是虚拟语气，表示对过去事情的假设，意思是本来能够做某事而没有
He could have passed the exam, but he was too careless.
本来他能够通过考试，但是他太粗心。

might have done
表示对过去事情的推测，might与may意思相同，但可能性更小。多用于虚拟语气结构中。
She might have achieved greater progress, if you had given her more chances.
如果你多给她点机会，她可能已经取得更大的成绩。

希望老师能帮到你