could have done

should have done,must have done都表示该做的没做,是虚拟语气,用于表达与过去的事实相反.但should have done语气上没有must have done重.它们有细微的差别.给你2个句子比较一下:
1)You should not have told him such a bad news when he was ill.
2)You mustn't have told him such a bad news when he was ill.
这2句话翻译过来可以是一样的,但是第1句的含义是,虽然你这么做错了,但是说话者并没有责怪你,责备你的意思,只是叫你注意,以后可不能这么做了.
而第2句话就可以是在责备你为什么要这么做,设想,如果说话者本来平时就和你关系不太好,第2句话甚至可以可以让你难堪,下不了台,对你进行报复.
总之,细微的差别就在语气之中.虚拟语气是英语学习的重难点,多加油哦!