—Can you ride a horse?—Sorry, I _____. But I can ride a bike very well.[ ]A. do B. don't C. can D. can't-七年级英语

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must 和 have to 的区别:must 表示说话人的主观思想,have to 表示客观需要。
3.need 是一个情态动词,他的用法完全和其他情态动词一样,但 need 还可当作实义动词使用,这时 need 就象其他动词一样,有第三人称,单复数, 后面加带 to 的动词等特性。
needn't + have + 过去分词 表示过去做了没必要做的事情。
4.dare 除用作情态动词外,更多的是当实义动词使用, 用法同实义动词一样,要考虑人称,单复数,时态等。
5.ought 应当,应该。后面跟带有 to 的动词不定式。
ought + to have done 句型。指过去动作,表示一件事情该做而未做。
ought not to have done 句型。表示一件不该做的事情却做了。
6.will (would)决心,愿望。 would 为 will 的过去式,
will, would用于疑问句表示说话人向对方提出请求或询问,用 would 比 will 更婉转,客气。
7.Shall、should 表示命令,警告,允诺,征求,劝告,建议,惊奇。
8.have to,不得不,必须,表示客观条件只能如此,而must 则表示主观思想。

  • 情态动词功能:
    助动词主要有两类:基本助动词和情态助动词。
    基本助动词有三个:do,have和be;
    情态助动词基本的有十四个:may, might; can, could; will, would; shall, should; must, need, dare, used to, ought to.had better 上述两类助动词的共同特征是,在协助主动词构成限定动词词组时,具有作用词的功能:
    1) 构成否定式:
    He didn't go and neither did she.
    The meeting might not start until 5 o'clock.
    2) 构成疑问式或附加疑问式:
    Must you leave right now?
    You have been learning French for 5 years, haven't you?
    3) 构成修辞倒装:
    Nowhere can he obtain any information about his sister.
    Hardly had he arrived when she started complaining.
    4) 代替限定动词词组:
    A: Who can solve this crossword puzzle?
    B: Tom can.
    A: Shall I write to him?
    B: Yes, do.

    情态动词表推测的用法小结   
    (一)情态动词表推测的三种句式    
    1.在肯定句中一般用must (一定),may(可能),might /can, could(也许,或许)。   
    (1)He must/may/might know the answer to this question?    
              他一定/可能/也许知道这个问题的答案。   
    (2)It is cold in the room. They must have turned off the heating.   
              屋里很冷,他们肯定把暖气关了。    
    2. 否定句中用can’t / couldn’t(不可能), may not/might not (可能不)。   
    (1)It can’t/couldn’t be the headmaster. He has gone to America.  这不可能是校长,他去美国了。   
    (2)He may not/might not know the scientist. 他也许不认识那位科学家。   
    3. 疑问句中用can/could (能……?)。    
     (1)Could he have finished the task? 他可能把任务完成了吗?    
     (2)Can he be at home now?  他现在能在家吗?   
    注:以上三种句式中情态动词的语气按程度都是依次递减的。Might, could并非may, can的过去式,而表示语气较为委婉或可能性较小。   

    (二)情态动词表推测的三种时态   
    1. 对将来情况的推测,用“情态动词 + 动词原形”。    
    (1)She must / may / might / could arrive before 5.  5: 00 前她一定/可能/也许到。    
    (2)She must/may/might/could walk miles and miles among the hills without meeting anyone.   
               她一定/可能/也许会在山里一连走好几英里而遇不到一个人。   
    2. 对现在或一般情况的推测,用“情态动词 + be”,“情态动词 +be doing”或 “情态动词 + 动词原形”。    
    (1)He must / may / might / could be listening to the radio now. 他一定/可能/也许正在听收音机。   
    (2)He can’t ( couldn’t ) / may ( might ) not be at home at this time. 这个时候他不可能/可能不在家。   
    (3)Mr. Bush is on time for everything .How can ( could ) he be late for the opening ceremony ?   
              布什先生一向准时,这次开幕式他怎么可能迟到呢?    
    3.对过去情况的推测,用“情态动词 + have +过去分词”。   
    (1)It must / may / might / could have rained last night .The ground is wet.  地湿了,昨晚肯定/可能/也许下雨了。   
    (2)The door was locked. He can ( could ) not / may ( might ) not have been at home . 门锁着,他不可能/可能不在家。   
    (3)Can / Could he have gotten the book? 难道他找到书了吗?    
    注:情态动词 should /ought to表推测时,意为“想必会,理应……”但与“have +过去 分词”连用时,则又可构成虚拟语气意为“本应该做某事却没做”。 
    例如:   
    (4)It’s seven o’clock. Jack should/ought to be here at any moment.   
         现在七点钟了,杰克理应随时到达。(推测)   
    (5)She should / ought to have attended your birthday party, but she had to look  after her mother in hospital. (虚拟)   
    她本该出席你的生日晚会的,可是她得在医院照顾她妈妈。   
    (6)Tom should not /ought not to have told me your secret, but he meant no harm.   (虚拟)   
    汤姆本不该告诉我你的秘密,可是他并无恶意。

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