英语学习单词need表示不必做和本不该做的区别

　　need 英语学习单词表示"不必做"跟"本不该做" 的区别：

　　didn't need to do表现： 从前不必做某事, 事实上也没做。.

　　needn't have done表示： 从前不必做某事, 但事实上做了。

　　英语学习单词例句：

　　John went to the station with the car to meet Mary, so she didn't need to walk back home. 约翰开车去车站接玛丽，所以她不必步行回家了。

　　John went to the station with the car to meet Mary, so she needn't have walked back home. 约翰开车去车站接玛丽，所以她本不必步行回家了。 (Mary步行回家，不遇上John的车。)

　　典型英语学习单词例题

　　There was plenty of time. She ___.
A. mustn't have hurried　 B. couldn't have hurried　　C. must not hurry　 D. needn't have hurried

　　答案D。needn't have done. 意为 "本不用"，即已经做了某事，而时实际上不必要。Mustn't have done 用法不正确，对过去发生的事件进行否定性推断应为couldn't have done, "不可能已经"。 must not do 不可能（用于个别当初时）的英语学习单词讲解。