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

　　我刚才没有听到电话，我一定是睡着了。

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

　　门锁着，他不可能在家。

　　(三)情态动词表推测的特殊用法

　　(1)can除了表示推测，用于疑问句和否定句中外，还可以用于肯定句中，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"，语气强烈。

　　If you must ask for a leave today, you must give out your reason.

　　如果今天你非要请假的话，你就得说出理由。

　　[即时演练2]

　　(1)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.

　　③It is important to know about the cultural differences that may cause (cause) problems.

　　(2)选词填空(must/may/might/can/can't)

　　①If you must go, at least wait until the storm is over.

　　②We enjoy good weather in January, but sometimes it can be terribly cold.

　　③I haven't decided where I'm going for my holiday. I may/might go to France.

　　④The story he told can't be true, because it is not reasonable.

　　⑤Can they finish this before the deadline?

　　二、should, could, would的用法

　　(一)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？