单选题 (Rarely) (we have seen) such an effective actor (as he) has proven himself (to be).
A. Rarely B. we have seen C. as he D. to be

【正确答案】 B
【答案解析】改为have we seen。rarely等否定副词放于句首时，后面要用部分倒装语序，即主谓倒装。