文档介绍：大学英语语法讲解情态动词的完成时(表示对过去的说法) ? must +have + 过去分词(用于肯定句)一定已经……. ? The light is still on. They must have forgotten to turn it off when they left the room. ?注:mustn ’ t have done × ? can ’ t (couldn ’ t) +have + 过去分词(用于否定或疑问句)不可能…….. ? He cannot have been to that town for I saw him just now. ? should/ought to +have+ 过去分词本应该做(却没有做)……. ? As his best friend, you should/ought to have helped him. (but in fact, you didn ’ t.) ? shouldn ’ t /ought not to +have +过去分词本不应该做(却做了)……. ? You shouldn ’ t have parked your car here, for it ’ s a public place. ? needn ’ t +have + 过去分词本不必做……? You needn ’ t have waited for me. I told you yesterday I would overwork . with ? with + done ? With the homework finished , the boy went out. ? with + doing ? With the old man leading the way, we finally find the house. ? with + prep ? With the light on , all the students went out of the classroom. 虚拟语气的用法?概念:表示说话人的愿望、假设、猜测、或建议,而不表示客观存在的事实。虚拟语气通过谓语动词的特殊形式来表示虚拟语气用于条件状语从句(1) 与过去事实相反? If… had + done, … would (should, could, might) +have +done ? If you had taken my advice, you wouldn ’ t have failed in the exam.