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情态动词can may must
情态动词表示说话人的感情和语气。它本身有一定词义,但不能单独做谓语,只有和实义动词一起构成谓语。情态动词没有人称和数的变化,后跟动词原形。下面我们把常用的 can may must的用法归纳如下:
1.(1)can 一般表示体,脑力方面的能力,意为“能,会(做某事)”,也可用来表示客观的可能性,意为“可以,可能”。例如:
He can swim in the river.
I can do the work myself.
The boy can sing in Englist.
I can help you with your housework.
(2)can \ could 也可以用于疑问句,否定句中表示“猜测”。如:He can't be at home.他不可能在家。
(3)can还能用来询问或请求一件事可以不可以做,常用于口语中,相当于may。例如:Can I help you? = May I help you?
can 的否定式是在其后加not? 写为cannot 或can't。例如:You can't stay here you can go home now.
2.(1)may一般表示“请求,许可,允许”。例如:
—May I come in﹖
—Come in please.
—May I go home now﹖
—Yes, you may.
You may only keep the books for two weeks.这些书你只可以借两个星期。
(2)may可以用来表示“猜测,推测”。例如:
Our head teacher may be in the office. 我们的班主任可能在办公室。
(3)may还能用来表示“希望,祝愿,渴望,请求和应该”。例如:
May you be happy? 祝你幸福!
3.(1)must表示义务,禁止和推测,意思是“必须,应该,应当,一定是,务必要”等。例如:
I must do my homework at once.
We must speak more English.
You must help each other.
It's ten now my mother must be angry.
(2)在回答must的疑问句时,其否定形式多用needn't?来表示“没必要,不许”。例如:
—Must she answer the question in Englist﹖
—No, she needn't.
注意:mustn't 经常表示绝对禁止,语气强烈。如:
You mustn't do it again.你再也不能这样做了。
(3)must在表示猜测,推测时,否定式常用can't代替。例如:
The students of Class Three must be having a good time in the park.三班的学生一定在公园玩得很高兴。
Tom must be in the classroom. 汤姆一定在教室里。
He cannot be ill.他不可能生病。
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