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'tB.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.canB.should

　　C.may D.must

　　3.-I stayed at a hotel while in New York.

　　-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.shouldD.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 haveD.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.mightD.need

　　4. ___________ it rain tomorrow, you would have to put off the visit to the Yangpu Bridge.

　　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 beB.must have been

　　C.should beD.should have been

　　2.Johnny, you ___________ play with the knife, you ___________ hurt yourself.(NMET'96)

　　A.won't; can'tB.mustn't; may

　　C.shouldn't; mustD.can't; shouldn't

　　3.Put on more clothes. You ___________ be feeling cold with only a shirt on.

　　A.canB.could

　　C.wouldD.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.mustB.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.mightB.should

　　C.can D.will

　　2.Peter ___________ come with us tonight, but he isn't very sure yet.(NMET'93)

　　A.mustB.may

　　C.canD.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.canB.willC.mayD.might

　　5.I thought you ___________ like something to read, so I have brought you some books.

　　A.may B.mightC.could D.must

　　(Key:ABADB)

　　(文/陕西西安市阎良区关山中学赵忠西；英语通高中一年级版03～04学年第2期；版权归英语辅导报社所有，独家网络合作伙伴新浪教育，未经许可，不得以任何形式进行转载。)