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can和could的基本用法经典解析知识点讲练 情态动词表示说话人在能力、必要、义务或猜测等方面的语气或态度，有自已的词义，但不能单独作谓语动词，必须和动词原形一起构成谓语动词，只有情态动词ought要和带to的动词不定式连用,将情态动词置于主语之前即构成其疑问式，在情态动词之后加not既构成其否定式。没有人称和数的变化。如：can, may, must, would, should, need, dare, might, used to 等。 1.can和could (could为can的过去式) 的基本用法 ①表示能力，如：He can speak English better than you. ②在疑问句和否定句中表示“怀疑”、“猜测”或“可能性”， ③表示“许可”时can可以和may换用， 如：You can (may) go home now. ④如果要表示语气婉转，可用could代替can，这时could不再是can的过去式， 如：Could you come again tomorrow? ⑤can和be able to都可表示能力，两者在意思上没有什么区别。但是can只能有现在式和过去式，而be able to则有更多的形式，且can指一般能力，able to 可表示具体能力 如：He will be able to do the work better. 语法易错题 英语单词记忆 高中英语教材 2、may和might (might为may的过去式)的基本用法 (1)表示允许或征询对方许可，有“可以”之意， 如：You may use my dictionary. 在回答对方说“可以做某事”或“不可以做某事”时，一般多不用may或 may not，以避免语气生硬或不容气。而用比较婉转的说法进行回答。 如：---- May I use this dictionary? ---- Yes, please. 或 ----Certainly. 在请求对方许可时，如果Might I…? 就比用May I…? 语气更婉转些， 如：May I have a look at your new computer? 但是表示“阻止”或“禁止”对方做某事时，要用must not代替may not， 如：---- May we swim in this lake? ---- No, you mustn’t. It’s too dangerous. (2)may或 might都可以表示可能性，表示“或许”、“可能”之意，如果用might表示可能性，则语气更加不肯定，如：They may (might) be in the library now . 3、must的基本用法 (1)must表示“必须”、“应该”之意，其否定式 must not，缩写形式为 mustn't，表示“不应该”，“不准”、“不许可”或“禁止”之意， 如：We must study hard and make progress every day. You mustn't touch the fire. 注意：对以must提出的疑问句，如作否定回答时，要用needn't或用don't (doesn't) have to (不 必)来回答，而不用mustn't，因为mustn't表示的是“禁止”或“不许可”之意 如：---- Must we finish the work tomorrow? ---- No, you needn't (don't have to), but you must finish it in three days. 在肯定句中must可以表示推测，表示“一定”或“必定”之意，如：---- Whose new bike can it be? ---- It must be Liu Dong's. I know his father has just bought him a new one. 作业： 1.___ I take the book out?—I'm afraid not. A. Will B. May C. Must D. Need 2.— May I take this book out of the reading room? —No, you___ . You read it in here. A. mightn’t B. won’t C. needn’t D. mustn’t 3 . I have told you the truth. ______ I keep repeating it? A. Must B.can C. May D. Will 4. -Must I buy a gift? -You___ buy a gift, but you can if you want to. A. must B. mustn't C. have to D. don’t have to 5. —I haven’t got the reference book yet, but I’ll have a test on the subject next month. —Don’t worry. You______ have it by Friday. A. could B. shall C. must D. may 6. I_______ have watched that movie —it’ll give me horrible dreams. A. shouldn’t B. needn’t C. couldn’t D. mustn’t 7.--- There were already five people in the car but they managed to take me as well. --- It ___ a comfortable journey. A. can’t be B. shouldn’t be C. mustn’t have been D. couldn’t have been 
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