may/must/can’t +have done +过去时间状语,表对过去情况进行推测,反义疑问句应用一般过去时.
It may/must have snowed last week, didn’t it?
he can’t have gone home last night ,did he >
may/must/can’t +have done 用于现在完成时表推测,反义疑问句应保留现在完成时.
He may /must have known the news, hasn’t he?
He can’t have done it, has he?
理解了吗?