四六級(jí)頻道為備考英語(yǔ)四六級(jí)的同學(xué)整理了《2019年12月英語(yǔ)四級(jí)語(yǔ)法知識(shí)：need "不必做"和"本不該做"》一文，希望可以為大家?guī)?lái)幫助，預(yù)祝大家高分通過(guò)本次考試!
2019年12月大學(xué)英語(yǔ)四級(jí)語(yǔ)法大全目錄
16.9 need "不必做"和"本不該做"
didn't need to do表示： 過(guò)去不必做某事, 事實(shí)上也沒(méi)做。.
needn't have done表示： 過(guò)去不必做某事, 但事實(shí)上做了。
John went to the station with the car to meet Mary, so she didn't need to walk back home. 約翰開(kāi)車去車站接瑪麗，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. 約翰開(kāi)車去車站接瑪麗，所以她本不必步行回家了。 (Mary步行回家，沒(méi)有遇上John的車。)
典型例題
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. 意為"本不必"，即已經(jīng)做了某事，而時(shí)實(shí)際上不必要。
Mustn't have done 用法不正確，對(duì)過(guò)去發(fā)生的事情進(jìn)行否定性推斷應(yīng)為couldn't have done, "不可能已經(jīng)"。 must not do 不可以(用于一般現(xiàn)在時(shí))。