问题
选择题
We __________ have proved great adventurers, but we have done the greatest march ever made in the past ten years.
A．needn’t
B．may not
C．shouldn’t
D．mustn’t
答案
B。
比较：needn’t have done意为“本来不必做某事”，may not have done意为“(过去)可能没有做某事”，shouldn’t have done意为“本来不应该做某事”(must表推测时不用于否定式)。根据句意，显然只能选B。