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 mustnt. Its 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 mustnt,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 mustnt touch the fire. (2)对以must提出的疑问句,如作否定回答时,要用neednt或用dont (doesnt) have to (不 必)来回答,而不用mustnt,因为mustnt表示的是禁止或不许可之意,如:---- Must we finish the work tomorrow? ---- No, you neednt (dont have to), but you must finish it in three days. (3)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 Dongs. I know his father has just bought him a new one.
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