(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

　　1．He must be ill.He looks so pale.

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

　　3．It can/could not be the headmaster.He has gone to America.

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

　　2．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.

　　5点前她一定/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"。

　　I didn't hear the phone.I must have been asleep.

　　我刚才没有听到电话，我想必是睡着了。

　　The door is locked.He can not have been at home.

　　门锁着，他不可能在家。

　　[即时演练2]　单句语法填空

　　①Listen，he must be reading(read)English.

②Since nobody gave him any help，he must have done(do) the research on his own.