一、can与could
1.can表示“能”、“会”时,指在脑力或体力方面所具有的能力;表示“可以”、“可能”时,指可能性;表示“可以”时,在口语中代替may,表示许可;can’t表示“不准”时,相当于mustn’t;用于否定或疑问句中,后面接动词不定式的完成式时,表示对过去发生的事的怀疑或不肯定;can’t后面接动词原形时,表示“不可能”,对现在表示推测。
2.could表示“能”、“会”,指过去在脑力或体力方面所具有的能力;表示“可以”时,用于一般疑问句,指客气地请求允许或求某人做某事,并不是过去时用法;用于if从句时,表示同事实相反的条件;could后面接动词不定式的完成式时,表示“责备”,对有能力做某事而没有去做提出婉转的批评;couldn’t后面接不定式的完成式,对过去表示推测。
[考题回顾]
1.Michael ___________ be a policeman, for he’s much too short.
A.needn’t B.can’t
C.should D.may
2.Mr Bush is on time for everything. How ___________ it be that he was late for the opening ceremony?(2001上海)
A.can B.should
C.may D.must
3.—I stayed at a hotel while in
—Oh, did you? You ___________ with Barbara.(NMET’98)
A.could have stayed
B.could stay
C.would stay
D.must have stayed
4.My sister met him at the Grand Theatre yesterday afternoon, so he ___________ your lecture.(2000上海)
A.couldn’t have attended
B.needn’t have attended
C.mustn’t have attended
D.shouldn’t have attended
5.If I ___________ go with you, I should feel very glad.
A.can B.could
C.should D.may
(Key:BAAAB)
二、should与ought to
1.should表示“应该”、“应当”,指有责任或义务做某事;后面接不定式完成式时,表示过去应该做而实际上没有做的动作;shouldn’t后面接不定式完成式时,表示过去不应该做而实际上已经做了的动作;后面接不定式的进行式(be+V-ing)时,表示“应该正在……”;should在肯定句中表示根据常规推测,某事应该发生;should用于条件状语从句的句首时,常省略if;should用于宾语从句中,表示虚拟语气,也可以省略。
2.ought to表示“应该”时,与should同义,但语气较强,强调有义务和必要做某事;如果后面接不定式的完成式,表示过去该做而未做的事;ought to的否定式是ought not to (=oughtn’t to),后面接不定式的完成式,表示过去不该做而已做了的事,也可以用来责备某人没有遵守规定。
[考题回顾]
1.There was a lot of fun at yesterday’s party.
You ___________ come, but why didn’t you?
A.must have B.should
C.need have D.ought to have
2.It’s nearly seven o’clock. Jack ___________ be here at any moment.(NMET’95)
A.must B.need
C.should D.can
3.—When can I come for the photos? I need them tomorrow afternoon.
—They ___________ be ready by 12:00.(NMET’98)
A.can B.should
C.might D.need
4. ___________ it rain tomorrow, you would have to put off the visit to the
A.Where B.Should
C.Would D.Will
5.One ought ___________ for what one hasn’t done.
A.not to be punished
B.to not be punished
C.to not punished
D.not be punished
(Key:DCBBA)
三、must与have to(have got to)
1.must表示“必须”、“应该”,指主观上认为应该做某事;表示“一定”、“准是”时,后面接be,表示对现在情况的肯定性推测;后面接be+V-ing时,表示对现在正在进行情况的推测;后面接不定式的完成式时,表示对过去情况的肯定推测;mustn’t表示“不许”、“不应该”。
2.have to表示“不得不”、“必须”,指在客
观条件下必须去做某事,多是被动的,在口语
中常用have got to替代;其过去式为had to
或had got to;可用于多种时态,否定式为
don’t have to,构成疑问句时,要借助do。
[考题回顾]
1.I didn’t hear the phone. I ___________ asleep.
A.must be B.must have been
C.should be D.should have been
2.Johnny, you ___________ play with the knife, you ___________ hurt yourself.(NMET’96)
A.won’t; can’t B.mustn’t; may
C.shouldn’t; must D.can’t; shouldn’t
3.Put on more clothes. You ___________ be feeling cold with only a shirt on.
A.can B.could
C.would D.must
4.I ___________ do all the difficult work for you.
A.haven’t got to B.not have go to
C.have got not to D.have got to not
5.You ___________ walk for miles and miles among the hills without meeting anyone.
A.must B.need
C.may D.should
(Key:BBDAA)
四、may与might
1.may表示“允许”、“请求”,常用于疑问句;表示“很可能”时,后面接动词原形,对目前动作有可能发生的推测;后面接be时,对目前可能存在状态的推测;后面接be+V-ing时,对有可能正在发生事情的推测;后面接不定式的完成式时,对可能已经发生事情的推测。
2.might表示“允许”、“请求”,语气较为婉转客气;后面接不定式的完成式时,表示对过去情况的推测,但把握性不大,语气较弱;用于虚拟语气中时,表示可能性,意即“可能”。
[考题回顾]
1.Sorry I’m late. I ___________ have turned off the alarm clock and gone back to sleep again.(2000春季)
A.might B.should
C.can D.will
2.Peter ___________ come with us tonight, but he isn’t very sure yet.(NMET’93)
A.must B.may
C.can D.will
3.He ___________ you more help, even though he was very busy.
A.might have given
B.might give
C.may have given
D.may give
4.If I had time, I ___________ go with you.
A.can B.will C.may D.might
5.I thought you ___________ like something to read, so I have brought you some books.
A.may B.might C.could D.must
(Key:ABADB)