1. must have done 表示对过去的推测：
That glass must have been broken by Xiao Ming.（打碎 这个动作发生在过去，所以不能光说must break）。
mustn't have done 不常见。
2.needn't have done 表示做了本不必要做的事情。如：
You needn't have called him then.
（你不必在那个时候给他打电话。--但是已经打过了）
比较一下：You needn't call him.（指：现在你不必给他打电话。）
3. couldn'have done 本来不能做的事情却做了。
He couldn't have finished reading such a long novel. I gave him the novel only yesterday.
4. shouldn't have done 本不该做的事情却做了。
You shouldn't have told him about it.
你不应该把事情跟他讲。
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