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情态动词must表推测用法归纳
（744406 甘肃省灵台县第三中学姚永清）
电话：150******** 情态动词must表推测，意为“必定，准是，很可能”。其用法归纳如下。
一、肯定推测的三种用法
1.“must + do”表示对现在情况的肯定推测。例如：
--Hi, Tom. Any idea where Jane is?
--She in the classroom. I saw her there just now. (2009重庆)
A. shall be
B. should have been
C. must be
D. might have been
析：因为“我刚看到了她”，所以可以推测出现在“她一定在教室里。”故选C。
2.“must + have done”表示对过去情况的肯定推测。例如：
The teacher have thought Johnson was worth it or she wouldnˊt have wasted time on him, I suppose. (2007安徽)
A. should
B. can
C. would
D. must
析：因为老师已经在他身上浪费了时间，所以可以判断出老师对Johnson的肯定推测发生在过去，故选D。
3.“must +be doing”表示对正在发生或将要发生的事情的肯定推测。例如：
There will be an English test tomorrow. He must be preparing for it now.
二、否定推测
对于否定情况的推测不能用“mustnˊt”, 而要用“canˊt”。例如：
1）You be hungry already---you had lunch only two hours ago!
(2008浙江)
A. wouldnˊt B . canˊt C . mustnˊt D. neednˊt
2）She have left school, for her bike is still here. (2008天津)
A. canˊt
B. wouldnˊt
C. shouldnˊt
D. neednˊt
析：1）是对现在情况的否定推测；2）是对过去情况的否定推测，故分别选B和A。
三、情态动词must表推测的反意疑问句
情态动词must表推测时，其反意疑问句不能用情态动词，而是必须去掉情态动词之后在句子本来意义的基础上进行反问。例如：
He must be helping the old man to water the flowers, ? (2009陕西)
A. is he B . isnˊt he C. must he D. mustnˊt he
析：这句话是对正在发生的事情的肯定推测，可以理解为“He is helping the old man to water the flowers,”所以反意疑问句为” isnˊt he”,故选B。