答案：C

题目分析：句意：只有辛勤的工作，你才能够期望成功。在句首的only如果后面跟了副词、介词短语或从句等状语，则主句用倒装结构。故选C.

点评：only置于句首的倒装情况要注意使用部分倒装，即将谓语动词部分置于主语前例如： Only when the war was over in 1918 was he able to get back to work．如only后跟的是主语，就不用倒装结构了。Only the teachers are allowed to use the room．（不倒装）