479　must/may/might/can't/couldn't have done

◎ 本句型用于对过去的推测，must have done意为“过去一定做了某事”；may/might have done表示“过去可能做了某事”；can't/couldn't have done表示“不可能已经做了某事”；本句型的疑问句和否定句要用can或could。在此句型中，用may和can语气较强，用might和could语气较弱，并无时态之分。

Jim lookes tired out. He must have sat up too late last night. 吉姆看上去非常疲惫，他昨晚一定睡得太迟了。

The light in his room is out. He might/may have gone to bed. 他房间里的灯熄了，他可能已经睡了。

You can't/couldn't have seen her yesterday. She went on an expedition a few days ago. 你昨天不可能看到她的，她几天前外出探险去了。

Frank looks worried. What may have happened to him？弗兰克看上去忧心忡忡的。他可能发生了什么事？