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【全额奖学金班】》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~
过去进行时是was/were doing，跟这里无关。
can't have been doing表示主动的动作，比如这里是主动看的
You can't have been working all the time. Did you have a favorite hangout spot?
你应该不会一直在学习，你有什么喜欢去的消遣的地方吗？

can't have been done表示被动的行为，比如
Now, the sheer numbers of these hand axes shows that they can't have been made for butchering animals.
这些手斧众多的数量表明它们不是用于屠宰动物。

祝同学学习进步~