didn t need to do表示: 过去不必做某事, 事实上也没做。.来源:考试大 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。来源:考试大 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 ___. 来源:考试大 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)。