It has been two years he came to China. A. sinceB. afterC. beforeD. till

问题补充：

It has been two years he came to China.

A. since

B. after

C. before

D. till

答案：

(答案→)A. since

B. after

C. before

D. till

解析：本题考查的是since引导的时间状语从句，since引导的从句为一般过去时，其主句为现在完成时，故选答案为A