We______ have proved【to be】 great 【advanturers—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
是选B.
句子实际可变为：
We may not have proved (to be+n/adj.可省略) great adventurers,but we have done the greatest march ever made in the past ten years.
句意：我们也许不是最伟大的探险家,但是过去十年中我们确实走过了最了不起的历程.
needn't have done 过去本来不必做（却做了）
may not have done 过去也许/可能不
shouldn't have done过去本来不应该做（却做了）
mustn't 禁止/不许做.表示肯定性推测判断时,要用于肯定句.否定句中常用can、could代替表示推测判断.
按照语义,只有B 最合适.