Question

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

Answer 1

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。