1） must表示必須，否定回答時(shí)用needn't. mustn't表示不許可。

　　「例如」

　　You must get to the station before 3， otherwise you will miss the train.Must I hand in my homework tomorrow？

　　No， you needn't. You can turn it in the day after tomorrow.

　　You mustn't smoke in the hospital.

　　2） must用于肯定句，可以表示推測(cè)，翻譯為：一定或想必。后面接動(dòng)詞的一般時(shí)，表示對(duì)現(xiàn)在的推測(cè)，接動(dòng)詞的完成式，表示對(duì)過去的推測(cè)。對(duì)過去的推測(cè)是考試的重點(diǎn)。

　　「例如」

　　She must live near here， for she comes to work on foot.

　　She was absent from class. There must have been something wrong with her.

　　The light was out. They must have gone to bed.

　　Mary's score on the test is the highest in her class. She ____ have studied very hard.（CET-4 1998.1）

　　A） may

　　B） should

　　C） must

　　D） ought to

　　“must +不定式完成式”表示對(duì)過去發(fā)生事情的推測(cè)。題意為：瑪麗的考試成績?nèi)�班第一，她學(xué)習(xí)一定很刻苦。答案為C.