外研版 (2019)必修 第二册Unit 1 Food for thought学案

Unit 1 Food for thought

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

1．be able to/can/could

[观察例句]

①This time I failed，but I'll be able to pass the exam next time.

②Mary can speak three foreign languages.

③He was able to leave Germany for America during the Second World War.

④Tom could sing English songs at the age of 6.

⑤What can they be doing there?

⑥He can't be in the classroom，for the light has been turned off.

⑦It can be quite cold at night here.

⑧—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只有现在式和过去式(could)。

[名师点津]

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)

①There's someone outside — who can it be?

②However great the difficulties may be，we can overcome them.

③The fire was very big，but all the people were able to escape from it.

④I can not give you details because I don't actually have any details.

⑤Could I have a word with you，if you're not too busy?

2．have to/must

[观察例句]

①Each student has to hand in a composition once a week.

②We must do everything step by step.

③You don't have to worry about me.I'm a good swimmer.

④That car is my property; you mustn't use it without my permission.

⑤He must be ill.He looks so pale.

⑥If 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mustn't表禁止。

(3)must表示推测，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)

①She has to do it herself.She has got no one to help her.

②They had/have to put off the sports meet because of the bad weather.

③Teachers must be patient enough with their students.

④This book must not be removed from the library.

⑤If you must smoke，please go outside.

3．had better

[观察例句]

①I think you had better go to the doctor about your cough.

②We 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3]　翻译句子

①你明天最好早点来。

You had better come early tomorrow.

②你最好别错过末班车。

You had better not miss the last bus.

4．dare/need

[观察例句]

①You needn't answer my question now.

②Need I tell him everything that has happened to his parents?

③He dared not tell his parents the truth.

④Dare he go home alone at night?

⑤He 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、否定句和条件从句中，dare有时态变化。另外，need和dare也可用作实义动词。

[即学即练4]　完成句子

①我喜欢周末，因为不必早起。

I love weekends，because I needn't/don't need to get up early．

②需要我马上把孩子们召集在一起吗？

Need I gather the children together at once?

③你怎么敢说我是贼呢？

How dare you say I am a thief?

④他问我是否敢摸大象。

He asked me if I dared touch an elephant．