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牛津英语9A第五单元语法（2）学案
学习目标：1.should 和ought to 与must区别
2.must 与have to
3.had better
4.Why not…?/Why don’t you …?
1.should 和ought to 与must区别
用should/ought to 可以表示“劝说”或“督促”， 和must 一样， 但三者语气强弱不同。
用should 语气比较肯定一些， 说话人的主观信心要强烈一些。含有责任的意思。
用ought to则口气上不那么坚定。
用must则在口气上最强烈，含有责任的意思。例如：
You must do your homework. You should speak to your parents politely..
I ought to write to him today.
2.must 与have to
must表示“必须”，侧重于说话人的主观意志。
have to 表示“必须”， 侧重于客观的需要，含有“不得不”的意味 。
3.had better (常缩写为’d better) ，是一固定词组， 表示“最好”， 用于表示对别人的劝告、建议或表示一种愿望。
had better 后面加动词原形，即 had better do sth.不论主语是第几人称, 句子无论是何种时态，had better 形式不变。had better 的否定形式为had better not do sth 表示“最好不要做……”。如：You’d better not miss the last bus.
You’d better not play on the road. It’s dangerous.
You’d better put on the coat. It’s cold outside.
4.Why not…?/Why don’t you …?
这两种句型结构常用于说话人向对方提出一个建议，意思是“不……？”； “为什么不……？”
Why not…?/ Why don’t you …? 后面必须跟动词原形。如：
Why not go swimming?=Why don’t you go swimming?
Why don’t you go out for a walk? =Why not go out for a walk?
练习：
一单项选择
1. My mother was ill. I ______ stay at home to look after her. A. must B. have to C. could D. can
2. ---____ go shopping with your father?--- That’s a good idea. A. Why don’t B. Why not C. Do D. Does
3. You ___ give up smoking.
A. would better B. had better C. would better to D. had better to
4. Why don’t you _____climbing with us tomorrow? A. to go B. going C. go D. goes
5. Cars, buses and bikes ___ stop when the traffic lights changes to red.
A. can B. may C. must D. need
6. It’s too hot. Perhaps you ______ swimming this afternoon. A. must go B. should go C. may go D. can go
7. To make our hometown more beautiful, you __throw rubbish into the river. A. needn’t B. mustn’t C. must D. need
8. How interesting the news is! Why _____ join us? A. won’t B. no C. don’t D. not
二、完成句子
1. You look so tired. ____________(你最好不要学习得太晚).
2. We____________(我们应该每天保持教室整洁和干净).
3. ___________ (或许我们可以向朱老师求助). He is kind and helpful.
4. ___________(你为什么不出去啊？) You should not study all the time.
5. ___________(你得保持安静) while reading in the library.
三、分别用should, ought to, had better, have to和 must完成句子
1.Wash your hands before dinner.
2.Make a wish when you blow out the candles on a birthday cake.
3.Drink cold water taken directly from the fridge.
4.Keep the table clean.
5.Eat vegetables even if you do not like them.
四、用why not和,why don’t you分别完成下列各句。
1.Go shopping with me.
2.Ask your family to turn off the TV while you are studying.
3.Share your problem with your parents.
4.Write to me if you are stressed.
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