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1、情态动词(1)一、情态动词的特征1情态动词表示说话人对某一动作或状态的态度，有一定的词义，但不能单独作谓语，必须和动词原形，即不带to的不定式连用，才能构成谓语。2情态动词没有人称和数的变化(have to例外，主语是第三人称单数时，要用has to)。二、情态动词的基本用法1be able to/can/could观察例句This time I failed，but Ill be able to pass the exam next time.Mary can speak three foreign languages.He was able to leave Germany for Ame
2、rica during the Second World War.Tom could sing English songs at the age of 6.What can they be doing there? He cant be in the classroom，for the light has been turned off.Everything can happen. Could I use your bike? Of course you can.归纳用法(1)表示能力。be able to和can都表示能力，意义上没有区别。但be able to可用于多种时态，而can只有现
3、在式和过去式(could)。注意：was/were able to表示经过一番努力，最后做成了某事；而could表示过去一般的能力。(2)表示推测。can表示推测，常用于疑问句和否定句，有时也可用于肯定句表示理论上的可能性，表示“有时候可能会”。could与can相比表示较小的可能性。(3)表示请求和允许。在问句中，could比can语气更委婉。即学即练1选词填空(be able to/can/could)Theres someone outsidewho can it be?However great the difficulties may be，we can overcome them.
4、The fire was very big，but all the people were able to escape from it.I cant give you details because I dont actually have any details.Could I have a word with you if youre not too busy?2have to/must观察例句Each student has to hand in a composition once a week.We must do everything step by step.You dont
5、have to worry about me.Im a good swimmer.That car is my property; you mustnt use it without my permission.He must be ill.He looks so pale.If you must go，at least wait until the storm is over.归纳用法(1)have to意为“不得不”，一般指客观，有时态和数的变化；而must意为“必须；应该”，一般指主观，没有时态和数的变化。(2)have to的否定式意为“不必”，而mustnt表禁止。(3)must表示
6、推测，意为“一定会”，只能用于肯定句。(4)if you must(do sth.)表示虽不赞同但可允许，意为“如果你一定要(那么做)”即学即练2选词填空(have to/must)She has to do it herself.She has got no one to help her.They had to put off the sports meet because of the bad weather.Teachers must be patient enough with their students.This book mustnt be removed from the l
7、ibrary.If you must smoke，please go outside.3dare/need观察例句You neednt answer my question now.Need I tell him everything that has happened to his parents?He dared not tell his parents the truth.Dare he go home along at night?He asked me if I dared ride a horse.归纳用法need和dare用作情态动词时，主要用于疑问句、否定句和条件从句，dare
8、有时态变化。另外，need和dare也可用作实意动词。即学即练3完成句子我喜欢周末，因为不必早起。I love the weekend，because I neednt/dont need to get up early需要我马上把孩子们召集在一起吗？Need I gather the children together at once?你怎么敢说我是贼呢？How dare you say I am a thief?他问我是否敢摸大象。He asked me if I dared(to)touch an elephant4had better观察例句I think you had better
9、 go to the doctor about your cough.We had better not remain here any longer.归纳用法had better do sth.意为“最好做某事”，否定形式为had better not do sth.即学即练4翻译句子你明天最好早来。You had better come early tomorrow.你最好别错过末班车。You had better not miss the last bus.用适当的情态动词填空1He wont be able to come again tomorrow because he is ve
10、ry busy.2You cant smoke here.Go out of the house if you must3He broke his leg and had to lie all the time.4She could play several instruments at the age of eight.5We had better not just talk .Lets go and help them.6Tony has known the good news，so you neednt tell it to him.7Parents are doing all they
11、 can to help their children achieve their ambitions.8As he was seriously ill，he had to stay in hospital.9He dare not do it because he is very afraid.10He cant be attending the meeting now because he has gone to Beijing on business.用适当的情态动词或括号内单词的适当形式完成短文Mary 1.could not read for very long with getti
12、ng a headache.Her best friend suggested her having an eye examination.“You 2.had better go to the Health Service and have your eyes 3.examined(examine)” her friend said.When Mary arrived at the Health Service，she found many people queuing up there.So she 4.had to wait for her turn.When it was her tu
13、rn，the doctor examined her eyes carefully and said，“I 5.dare say you dont pay attention to 6.protecting(protect) your eyes.But you 7.neednt/dont have to worry about it.Use some medicine and dont make your eyes too tired，and soon you will 8.be able to recover.”This experience taught Mary the 9.importance(important) of protecting eyes.She told her best friend，“There is nothing serious with my eyes，but from now on I 10.must try to protect my eyes.”