📌 推测程度（过去）
must have been → 90%以上把握（一定是）
can't have been → 90%以上否定把握（不可能）
may have been → 约50%把握（可能）
might have been → 约30%把握（也许）
📌 现在推测 vs 过去推测
现在：He must be tired. 他现在一定很累。
过去：He must have been tired. 他当时一定很累。
现在：He can't be at home. 他现在不可能在家。
过去：He can't have been at home. 他当时不可能在家。
📌 例句对比
He must have been in a hurry. 他一定很匆忙。
He may have been late for work. 他可能上班迟到了。
He can't have been asleep. 他不可能在睡觉。
He might have been joking. 他也许在开玩笑。