Question

【题目】Li Hua has been back to his hometown twice he moved to Shanghai．

A. before B. when C. till D. since

Answer 1

【答案】D

【解析】句意：李华自从搬到上海，他已经回过他的家乡两次。before在……之前；when当……时候；till直到；since自从。根据Li Hua has been back to his hometown twice可知主句用了现在完成时。since引导的从句表示从过去时间开始持续到现在的动作，故与现在完成时连用，故选D。