情态动词＋have done1.表对过去的推测：(1) must have done：意思是“一定已经”。 If he had really been there，I must have seen him. 如果他当时确实在那里，我一定会看见他。
1.must表示必须、义务等,相当于have to, 但must强调主观因素,而have to强调客观因素。I must go to see a doctor.我得看医生去。2. need可以对MUST引导的一般疑问句作否定回答。Really?
句型1would rather that somebody did…“宁愿……;更愿意……”(表示现在或将来的愿望)would rather that somebody had done…“宁愿……;更愿意……”(表示过去的愿望)[例句]I'd rather you posted
