-----you realize that you were dirving at 80 miles per hour,don't you-----no officer,i ___.this car can't do more than 70.a.don't need to beb.may not have beenc.couldn't have beend.needn't have been

-----you realize that you were dirving at 80 miles per hour,don't you-----no officer,i ___.this car can't do more than 70.a.don't need to beb.may not have beenc.couldn't have beend.needn't have been
-----you realize that you were dirving at 80 miles per hour,don't you
-----no officer,i ___.this car can't do more than 70.
a.don't need to be
b.may not have been
c.couldn't have been
d.needn't have been

-----you realize that you were dirving at 80 miles per hour,don't you-----no officer,i ___.this car can't do more than 70.a.don't need to beb.may not have beenc.couldn't have beend.needn't have been
答案为C.
此题考查情态动词表示推测性的用法.
在肯定句中,表示现在“一定”用must（语气最强）,may和might（语气最弱）+动词原形；表示过去的时间,用must/may/might have done
在否定句中,表示现在“一定不,不可能”用can‘t,couldn't + 动词原形；表示过去的时间,用can/could + have done.
从句意来看,警察说车速超过80了,回答说“不可能,我的车最快不能超过70”
所以,答案为C.