人教版book3unit2HealthyeatingGrammar.doc

1、should 和 ought to 的用法(1). should, ought to都可表示“应该”。ought to用于表示按道理应当，常指客观的义务或责任，大多数情况下可用should代替，但比should语气重。如：I should help her because she is in trouble.You ought to take care of the baby.(2).表示劝告、建议或命令时，should和ought to可通用，但在疑问句中常用should。ought to的否定式为oughtnt to或ought not to。如：You should / ought to go to class right away.Should I open the window?What should we do next?(3) should, ought to都可表示推测。如：He ought to / should be home by now. This is where the oil ought to / should be. 注：should 和ought to 后面跟动词不定式的完成式, 其肯定句表示“过去应该做而未做”, 其否定句则表示 “过去不该做但做了”。You should/ought to have made the decision a week ago.I shouldnt have made such a foolish mistake. 多数情况下，ought to可与should互换使用。ought to的反意疑问句用shouldnt替代。例：You ought to have helped him with his English, _?A. wont you B. ought not youC. shouldnt youD. wouldnt you2、must 和 have to (1).must的用法 表示主观的义务和必要,主要用于肯定句和疑问句,意思为“必须，得，要”；由must引起的疑问句，肯定回答要用must或haveto,否定回答要用neednt或donthaveto,意思是“不必” ； must的否定形式mustnt表示禁止，意思是“不能，不许”。如： MustIfinishthetaskrightnow? 我现在必须完成这个工作吗？ Yes,youmust./Yes,youhaveto. 是的。 (No, you neednt. / No, you dont have to. 不，不必。) You mustnt come here without permission. 未经允许，你不能来这儿。Mother is out, so I have to look after the shop. 妈妈不在家，因此我不得不照看商店。 【例】The boss has given everyone a special holiday, so we _ go to work tomorrow. (上海 2007春)A. cant B. mustntC. neednt D. shouldnt【点拨】考查情态动词。根据题意, 可知这里表示“没有必要”, 故只能选C项。(2).have to 的用法1) must表示一种主观的需要，而haveto表示一种客观的需要，意思是“不得不”。如： I have to attend an important meeting this afternoon. 今天下午我不得不参加一个重要的会议 Mother is out, so I have to look after the shop. 妈妈不在家，因此我不得不照看商店。 haveto的否定形式是dont have to, 相当于neednt。如： They dont have to buy a computer at present. 他们目前没有必要买电脑。【例】The boss has given everyone a special holiday, so we _ go to work tomorrow. (上海 2007春)A. cant B. mustntC. neednt D. shouldnt【点拨】考查情态动词。根据题意, 可知这里表示“没有必要”, 故只能选C项。【例】What do you think we can do for our aged parents?You _ do anything except to be with them and be yourself. (重庆 2007)A. dont have to B. oughtnt toC. mustnt D. cant 【点拨】根据题意“除了和他们呆在一起做你自己外, 没有必要做任何事情。”可知这里选择dont have to表示“不必”。故选A项。3. must和needneed作情态动词时, 只能用于疑问句和否定句。构成否定句和疑问句时不借助于助动词do。 Need I finish the work today? Yes, you must. / No, you neednt.b. must的肯定形式表示“必须”，否定式 表示“禁止、严禁”。 You must come here. You mustnt take the book away from the library. 单选练习题1. I lived with my sister this summer and didnt have to pay rent. So I _ save most of my salary. A. was able to B. would C. could D. should2. I promised to get there before 5 oclock, but now the traffic is still so heavy. They _ for me impatiently. A. may wait B. must be waiting C. could wait D. ought to wait3. I _ her, but I never could. A. ought to help B. must help C. must have helped D. ought to have helped 4. The Smiths went to the country for the weekend as they _ to the office. A. neednt have gone B. mustnt go C. may not go D. didnt have to go5. My parents never remember my telephone number, and they always _ look it up. A. should B. can C. have toD. must6. Bobby _ me your secret, but he meant no harm. A. shouldnt have told B. should tell C. mustnt have told D. could tell 7. If you _ go, at least wait until the rain stops. A. can B. must C. should D. would8. You _ follow me if I am wrong. A. must B. dont have to C. wouldnt D. ought to 9. _ you like to have a walk with us this evening? A. Could B. Will