前面給大家講解了公共英語等級考試pets3語法必備知識點名詞性從句，本節(jié)我們繼續(xù)為大家講解pets3相關(guān)的語法：虛擬語氣。供大家學(xué)習(xí)參閱。
9 need "不必做"和"本不必做"
didn't need to do表示過去不必做某事, 事實上也沒做。
needn't have done表示過去不必做某事, 但事實上做了。例如：
John went to the station with the car to meet Mary, so she didn't need to walk back home.
約翰開車去車站接瑪麗，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.
約翰開車去車站接瑪麗，所以她本不必步行回家了。 （Mary步行回家了，沒有遇上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，而時實際上不必要。
Mustn't have done 用法不正確，對過去發(fā)生的事情進行否定性推斷應(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）。
9 need "不必做"和"本不必做"
didn't need to do表示過去不必做某事, 事實上也沒做。
needn't have done表示過去不必做某事, 但事實上做了。例如：
John went to the station with the car to meet Mary, so she didn't need to walk back home.
約翰開車去車站接瑪麗，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.
約翰開車去車站接瑪麗，所以她本不必步行回家了。 （Mary步行回家了，沒有遇上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，而時實際上不必要。
Mustn't have done 用法不正確，對過去發(fā)生的事情進行否定性推斷應(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）。