(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？

　　[名师点津]　若表示过去的特定能力(即在过去特定场合做某事的能力)，则不能用could，而用was (were) able to do sth.或用managed to do sth.或用succeeded in doing sth.等。

　　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。

　　He could have gone home.

　　 他可能已回家了。

　　3．比较委婉客气地提出问题或陈述看法。

　　Could you drive me to the station?

　　你可以开车送我去车站吗？

　　We could take the train or alternatively go by car.

我们可以坐火车去，也可以坐汽车去。