“Can…have done”意為“難道真的做了嗎”，表示不相信。

例如：

　　Can they have left so soon?

　　難道他們這么快就走了?

　　Can he have done such a foolish thing? (= Is it possible …?)

　　他會(huì)做這樣的傻事嗎？

　　Can she have lost the money? (=I doubt whether…)

　　她可能丟失了那筆錢嗎？

　　Could he have left the work unfinished?

　　他會(huì)丟下工作不干了？