或"情态动词＋动词原形"。

　　He must/may/might/could be listening to the radio now.

　　他一定/可能/也许正在听收音机。

　　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"。

　　It must have rained last night. The ground is wet.

　　地面湿了，昨晚肯定下雨了。

　　He cannot have been to that town.

　　他不可能去过那个镇。

　　3．情态动词表推测的特殊用法

　　(1)can除了表推测，用于疑问句和否定句中外，还可以表示"在某段时间内一时的可能性"。

　　It can be quite windy there, especially in spring.

　　那里有时容易刮风，特别在春季。

　　(2)must表示"一定，非得；偏要"，强烈语气。

　　If you must smoke, you can smoke in that room.

　　如果你偏要吸烟，你可以在那个房间吸。

　　集中演练1

　　用适当的情态动词填空

　　①Life is unpredictable; even the poorest may/might become the richest.

　　②My uncle can't be at home, for he has gone to Beijing on business.

　　③Since nobody gave him any help, he must have done the research on his own.

　　④I haven't decided where I'm going for my holiday. I may/might go to France.

　　⑤-Look, someone is coming. Who can/could it be?

　　-I think it must be Tom, because he said he would be here at this time.

　　1.could的用法

　　(1)表示过去一般的能力(即想做某事就随时可以做某事的能力)。

　　Could you speak English then?

　　那时候你会说英语吗？

　　[名师点津]　若表示在过去特定场合做某事的能力，则不能用could，而用was/were able to。

　　The fire was very big but everyone was able to escape from the building.

　　火势很凶猛，但大家都逃了出来。

　　(2)could表示推测，表示某事有可能发生或可能是事实。在肯定句中没有must那么有把握；在否定句中没有can't那么有把握。

　　He couldn't be a bad man.

　　他不大可能是坏人。

　　(3)could还可以用于表示客气、委婉或礼貌的请求语气。

　　Could you pick me up at the airport at 5 a．m. next Monday?

　　下周一早上五点你能到机场接我吗？

　　I'm afraid that we couldn't give you any definite answer at this moment.

恐怕我们这时还无法给您任何确切的答复。