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1、动词（情态动词）(ought to,have to,need),1.ought toought to 应该,与should比较ought to语气重，多表示责任、义务，道德，法律等方面。Young people should learn how to use computers.年轻人应该学习怎样使用电脑。Every citizen ought to obey law.每个公民都要遵守法律。You ought not to go.你不应该走。,ought to 的否定形式为ought not 或oughtnt to，其一般疑问句形式为将ought置于主语前。,eg You ought not
2、to do it?,你不应该做这件事。,-Ought you to go to the hospital?你应该要去医院吗？-Yes,I ought(to)-是的，我要去。,2.have to,have to不得不。有时态和人称的变化，其否定形式和疑问形式需要借助助动词do。,eg:I have to go home now.,(肯定句）,You dont have to go home now.,(否定句）,我不得不回家了。,你不用现在回家。,When do you have to go home?,(疑问句）,你什么时候要回家？,I had to go home at that time.
3、,(过去式）,我那时候不得不回家。,3.need1.作情态动词时,仅用于否定或疑问句,后接动词原形,无人称和数的变化，表“需要”。You neednt return the book now.Need he start from the beginning?Yes,he must./No,he neednt/doesnt have to.,2.neednt have done 表示做了本不必要做的事情,意为“本不必要而做了”。He neednt have gone there yesterday.你昨天其实不必要去那儿的。3.need作实义动词时,表示“需要”，有人称、时态和数的变化。He n
4、eeds to finish it this evening.The classroom needs cleaning.,可兼作实义动词的情态动词：need1.作为情态动词用，常用在否定句和疑问句中。Need+S(主语)+V(动词原形)S+neednt+VNeed he go yesterday?You neednt return the book now.,2.作实义动词用，常用在肯定句中,有人称、时态和数的变化。He needs to go there himself.他需要自己去那里。He has grown up,so we dont need to worry about him.他
5、已经长大了，因此我们不必要再担心他了3.sth.(sb.)need(want,request)+doing/to be done.The house needs cleaning/to be cleaned.这个房子需要打扫,4.情态动词+have done,.must have done 用于肯定句，表示“过去一定做过某事”。,eg.She mush have played badminton yesterday morning.她昨天早上一定是去打羽毛球了。,can have done 一般用于疑问句和否定句，用于表示对过去发生事情的可能推测。could have done 用于肯定句时，
6、表示“本有能力做某事而未去做。,eg.He can not have had lunch in this restaurant yesterday.He was in America at that time.他昨天不可能是在这家餐厅吃饭。他那时候在美国,She could have finished his homework today.她今天本来可以完成家庭作业的,should(ought to)have done.表示“过去本应该做某事而（实际上）没有做”，含有责备或遗憾的语气；其否定形式,表示某种行为不该发生的却发生了。,eg They ought to have gone to th
7、e classroom earlier.他们应该早一点去教室。,eg You ought not to have drank so much beer.你不应该再喝这么多啤酒。,.might/may have done,表示对过去发生的动作进行表示可能性的推测。意思是“也许已经做过了某事，可能已经做了某事”，多用在肯定句中，might的语气更加不肯定。,eg He may have gone to the clinic.他可能去医务室了。,He might have read about the news in the newspaper.他可能已经从报纸上知道这个消息了。,.neednt have done 表示做了本不必要做的事情而实际上做了。意为“本不必要而做了”。eg Our color TV set is still good enough.You neednt have bought a new one.我们的彩色电视机已经够好了。你不必要再再买一台新的。,
