<例句>
Can it be true?
这可能是真的吗?
<语法分析>
情态动词和原形动词连用可以表示对现在情况的推测，情态动词和现在完成时态连用表示对过去情况的推测。can可以用于肯定句、否定句和疑问句中，may也可用在肯定句和否定句中，但不用在疑问句里。must和have to只用在肯定句里。should (could, might, ought to) + 过去分词，可表示“原本......而未......”的意思。
<触类旁通>
(1) It cannot have been lost in the post.
它不可能落在邮筒里。
语法分析：can和现在完成时态连用，表示对过去情况的推测。
(2) She cannot be his wife.
她不可能是他的妻子。
语法分析：情态动词和原形动词连用可以表示对现在情况的推测。
(3) That may be so, but I doubt it.
事情可能就是这样，但我对此表示怀疑。
语法分析：may用在肯定句和否定句里，但不用在疑问句里。
(4) He must be in.
他一定在家。
语法分析：must 只用在肯定句里。
(5) I should have gone there alone.
我本该一个人到那里。
语法分析：should或could might ought to + 过去分词，表示“原本......而未......”的意思。
<巩固练习>
1. She could not _____[see] me yesterday because I wasn't there.
2. Could he _____[hear] of her?
3. It may _____[be] your mistake.
4. English may ____[hard], but it's so useful.
5. She may _____[go] somewhere else.
6. She might not ____[mad].
7. She must _____[read] in the reading-room.
8. They should _____[arrive] there by this time.
9. You might _____[complete] the work earlier.
10. You ought to _____[give] me something to eat then.
<参考答案>
1. have seen 2. have heared 3. have been 4. be hard 5. have gone 6. be mad 7. be reading 8. have arrived 9. have completed 10. have given
