单选题 (Should) John resign and Henry (succeed) him, we (would have had) a (more) vigorous leadership.
【正确答案】 C
【答案解析】改为would have。这里是表示对将来发生的事情的假设，为虚拟语气。其条件从句用动词过去时，主句是用情态动词的过去时+原形动词。should John resign的正常句式为if John should resign，省略if时要将情态动词前置，进行倒装。