The whole Chinese people will never forget the day May 12th the strong earthquake

问题补充：

The whole Chinese people will never forget the day, May 12th, , the strong earthquake happened in Wenchuan.

A. on which

B. on that

C. in which

D. from which

答案：

(答案→)A. on which

B. on that

C. in which

D. from which

解析：考查定语从句的用法。on which 在此表时间，相当于when。