同学你好，该知识点来自沪江网校《英语零基础直达大学六级全能畅学卡【现金奖励班】》的课程，想要更系统的学习，欢迎进入课程学习。不仅可以和更多的同学一起学习，而且还有老师、助教随时的学习指导和知识点解答哦。

同学你好～

must have been 表示过去的【状态】；
must have done 表示过去发生过了的【动作】。

must have +done sth，对过去时间里可能发生的事情的推测，语气较强，具有肯定，谅必的意思。
例如：
　---Linda has gone to work, but her bicycle is still here.
　---She must have gone by bus.
must have been 也是 must have done 的一种，因为been就是am/is/are的过去分词，例如：
It must have been the coffee that kept me awake. 一定是喝了咖啡，使我睡不着。
He must have been awake all night. 他一定一夜没睡。

希望可以帮到你～祝你学习进步！