The thought that she might be ill annoyed him.

　　想到她或许病了，他就不安。

　　2．否定句中用can't/couldn't(不可能)，may not/might not(可能不)。

　　If Tom didn't leave here until five o'clock, he can't be home yet.

　　如果汤姆五点才离开这儿，他此时一定还未到家。

　　He said that I might not borrow his car.

　　他说我可能不用借他的车。

　　3．疑问句中用can/could(能......？)。

　　Could he have finished the task?

　　他可能把任务完成了吗？

　　Can he be at home now?

　　他现在能在家吗？

　　[即时演练1]　用适当的情态动词填空

　　①He must be ill. He looks so pale.

　　②He was afraid they might not agree with him, but I am not quite sure.

　　③It can't/couldn't be the headmaster. He has gone to America.

　　④Someone is knocking at the door. Who can it be?

　　⑤It may take a long time to find a solution to the problem.

　　(二)情态动词表推测的三种时态

　　1．对将来情况的推测，用"情态动词＋动词原形"。

　　She must/may/might arrive before 5：00 p．m.

　　下午5：00前她一定/可能/也许到。

　　2．对现在或一般情况的推测，用"情态动词＋be""情态动词＋be doing"或"情态动词＋动词原形"。

　　At this moment, our teacher must/may/might/could be correcting our exam papers.

　　这时，我们老师一定/可能/也许在批改试卷。

　　Mr. Bush is on time for everything. How can/could he be late for the opening ceremony?

　　布什先生一向准时，这次开幕式他怎么可能迟到呢？

3．对过去情况的推测，用"情态动词＋have＋过去分词"。