1.I didn't go to class last night because my car broke down.

﹣You _______ mine. I wasn't using it.

答案里有两个让我感觉迷惑的选项could have done和may/might have done.我看薄冰写的只能选择could have done表示本来可做却没做的事，这里应该可以用may/might have done吧，它们两个应该和could have done应该都可以表示推测或者虚拟吧，这里如果虚拟，这三个意思不都是本可能的意思吗？

2.A three-good student ________ have done such a thing.

答案里有could not, may not和might not，可以是选了could not,解释是英语里一般不会用may和might的否定完成式，请问是为什么呢？

3. He  _may have missed_ the train.说划线部分不能用may not have been, 要说不会误了得用can的否定完成式，难道用用may not have missed可能有两个意思，可能不会(推测)和本可能不会(虚拟)，才不能用的吗

我觉得这三个题有一定共性，期待老师的解答。