同学你好，该知识点来自沪江网校《新概念英语1、2、3、4册连读标准会话【随到随学班】》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 done sth.一定做过某事。表示对过去事情的较有把握的推测
From what you said, she must have told you all about it.
从你的话看，她一定告诉了你所有的事情。
The light was out. They must have gone to bed.
灯都熄了，他们必定睡了。

would have done 本可能做某事，实际没做
He would have come if you had phoned him.
要是你给他去了电话，他会来的。
I would have soon found the one I wanted if the books had kept in order.
如果书籍摆放整齐了，我本可以很快就会找到我想要的那本书了。

要不是你，我有可能就失败了，这符合would have done的意思。

祝同学学习进步~