情態助動詞

must和其他的情態助動詞用法相同：不隨主詞作變化、後面接原形動詞。「一定」表肯定的推測： 1、現在：S ＋ must ＋原形動詞... 如：You must be Michael. Jenny talks about you all the time. （你一定是 Michael。Jenny 時常提到你。） 2、過去：S ＋ must ＋ have ＋ p.p.... 如：Wilson fell asleep in class today. He must have stayed up until very late last night. （Wilson 今天在課堂上睡著了，他昨晚一定熬夜到很晚。）「必須」：Students must follow school rules.（學生必須遵守校規。）