表示推测的用法 can , could ,may ,might ,must 皆可用来表示推测.其用法如下: a．could ,might 表示推测时不表示时态.其推测的程度不如can ,may. b．can ,could 用于否定句和疑问句中. 句型:主语+ can't , couldn't +be +动词ing． Can ,Could +主语 +be +动词 ing． They can't be cleaning the room now．他们现在不可能在打扫房间. c．may ,might , must 用在肯定句中. 句型:主语+ may ,might ,must +be +动词 -ing (表示对现在发生动作的推测) He must be sleeping . 他现在肯定在睡觉. d．但如果上述这些词 + have +过去分词则指对过去已发生的事进行推测. The road is wet. It must have rained last night . 地是湿的,昨天晚上肯定下雨了. There isn't any water on the road . It couldn't have rained last night . 地面上一个水滴都没有.昨天不可能下雨了. (四) have to的用法 【
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