高考英語語法講解及練習
Model Verbs: 情態動詞
一. 表示許可：有may, might, can, could。其中might. could則語氣較委婉，但回答由他們引起的問句時，則不用might, could而用can。
1) May Might Can Could I keep the book for a few days? Yes, you can.
否定形式可用may not, can not或must not，不用might not。
2)Visitors may not (或can not/mustn't) touch the button.
二、表示能力：can; be able to. be able to用于各種時態。在一般過去時中，若指“能夠并且通過某種努力完成某樁事”，我們必須用be able to。
1) Cats can are able to climb trees very quickly.
2) A big fire broke out last night, but everyone was able to escape from the house.
三、表示“責任和義務”的情態動詞有must(主觀),have to(客觀)。mustn’t 表示“不可以、不允許”，而have to否定形式：not have to/ needn't。
1) As there was no bus, we had to walk back home. (客觀條件)
2) You mustn't shout like that to your parents. (不可以、不允許)
3) You don't have to needn’t work if you don't feel well.
四、用于推測：must, may, might, can, could . 但疑問句中只能用can, could.
1) He looks pale. He__________ be ill.
2) ---Who _____it be? It _____(not) be Mr. Smith, for he has just left for Paris.
---It ________be Mr. Brown, for he has something to discuss with me.
3) He said he didn't feel very well. He _____(not) come to the meeting this evening.
(1.must 2. can, can’t, must 3. maymight not)
▲注意: 表推測時 must, should (ought to) , may, could , might 可能性依次遞減。should, ought to “應該…”較多地用于預測將來的事。can表示理論上的可能性，用于泛指.may, could, might表示事實上的可能性，用于特指具體的，可能將要發生的事。
1) He should be back by now. 他現在該回來了。
2) The teacher has explained it several times. There ought to be no problem for them.
4) A dog can be dangerous to you 狗可能給人帶來危險。(有這種可能性)
This dog is very clever. It may (或might/could) help you find your key.
這條狗非常聰明，他可能會幫助你找到鑰匙。指具體的事有可能發生。
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