used to 过去常常（现在已不再） used not/usedn't/usen't to do

didn't use to do Used...to do...?

Did...use to do...? Yes,...used.

No,...use(d)n't.

Yes,...did.

No,...didn't. II.情态动词的重点知识

表示"能力、许可"的can和may 表示能力的情态动词用can/could A computer_____think for itself; it must be told what to do.

A.can't B.mustn't C.may not D.might not 表示许可时用may/might ,can/could 都可以，但在问句中用could...?或might...？ 以使口气委婉客气，其回答一定要用can或may，以使回答口气明确（must表示一定，必须，mustn't表示禁止，不许可）。 ①-Could I call you by your first name? -Yes, you______

　A.will B.could C.may D.might

②Johnny, you_____play with the knife, you_____hurt yourself.

　A.won't/can't B.mustn't/may

　C.shouldn't/must D.can't/shouldn't 在肯定句中could不可以用来表示过去某一特定场合的能力，而要用was/were able to。 The fire spread through the hotel very quickly but

everyone_____get out.

A.had to B.would C.could D.was able to 表示"推断、判断"的can

may,must 在肯定句中都可以用来表示可能。在含义上must语气最肯定,may表示的是事实上的可能性。 Peter______come with us tonight, but he isn't very sure yet.

A.must B.may C.can D.will

而can表示的是逻辑上的可能性：

Mary is in poor health. She can be ill at any times. 在否定句中只能用can和may。所以can't时用以代替mustn't，语气比may更肯定。中文可以翻译为不可能。 Michael______be a policeman, for he's much too short.

A.needn't B.can't C.should D.may 在疑问句只能用can，不能用may和must。 He may be very busy now. Can he be very busy now?

He must be very busy now. Can he be very busy now? need need作为情态动词只有一种形式，只用于否定句和疑问句。 dare dare作为情态动词用时有两种形式：dare和dared两个词形，除了可以用于否定句和疑问句外，还可以用于条件从句或表示怀疑的句子中。 If he dare come,I will kick him out. I don't know whether he

dare say.

注意:He doesn't dare(to)answer the question.（否定句）

Does she dare(to)enter the dark room?（疑问句） shall 用于第一人称：征求对方的意见。 What shall we do this evening? 用于第二、三人称：警告、命令、允诺、威胁等。 You shall fail if you don't work harder. 警告

He shall have the book when I finish reading.允诺

He shall be punished.威胁 should 劝告、建议、命令、应该做、道义上的责任。 You should(ought to) go to class right away.

I should(ought to) help him because he is in trouble.