我们都知道，在大学英语四级考试中，单独考察英语四级语法的题型很少，但是英语四级语法知识点却贯穿整张试卷，下面是新东方网英语四级频道为大家整理的大学英语四级语法知识，希望可以为大家带来帮助。
2017年12月大学英语四级语法大全目录
16.9 need "不必做"和"本不该做"
didn't need to do表示： 过去不必做某事, 事实上也没做。.
needn't have done表示： 过去不必做某事, 但事实上做了。
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，没有遇上John的车。)
典型例题
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"本不必"，即已经做了某事，而时实际上不必要。
Mustn't have done 用法不正确，对过去发生的事情进行否定性推断应为couldn't have done, "不可能已经"。 must not do 不可以(用于一般现在时)。
2017年12月大学英语四级语法大全目录
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