三、must + have + -ED 分词：用于肯定句，表示对过去情况一种肯定推测，表示“肯定，一定。”

You look so sleepy.You must have sat up late last night.你看上去这么因倦，昨晚一定睡得很晚。

Johny is always showing numerous little attentions to Marythese days.He must have fallen in love with her.约翰尼这些天总是向玛丽大献殷勤，他一定爱上她了。