2018年大学英语B级语法之情态动词
情态动词用来表示能力、允许、许诺、可能、必须、劝告、意愿等概念或态度。情态动词无人称变化，在句子中和动词原形一起组成谓语。常用的情态动词有must，can，be able to，need，shall, should(ought to), could，would。
注意：mustn’t的意思是“禁止”，needn’t的意思是“无须，不必”。
情态动词后接完成时的用法
must+现在完成时结构:这一结构表示对过去一个动作比较有把握的猜测
例:I believe he _______ an accident, otherwise he would have arrived on time.
A. would have had
C. should have had
B. could have had
D. must have had
答案为D
2. should (ought to )have done用来表示本来应该做却没有做的事情。
例1:I'm sorry I couldn't get in touch with him before he left,____him earlier.
A. had a telephone B. have phoned
C. should have phoned D. should be phoned
答案是C
例2: You ought_______the matter to the manager the day before yesterday.
A. to report
B. to have reported
C. to reporting
D. have reported
答案:B
3.could+现在完成时，表示本来能做的事情而没有做。
例:Mary_____that coat, but she chose to lend the money to a needy neighbour.
A. could have bought B. must have bought C. can buy D. could buy
答案为A.
4.needn't+现在完成时，表示本来不该做的事情却做了。
例:I dressed very warmly for the trip, but I needn't have done so. The weather was hot.
小编推荐：
更多大学英语B考试资讯>>>大学英语B考试
想要顺利通过大学英语B考试吗？考无忧网校助你顺利通关大学英语B考试>>>大学英语B考试题库
