I arrived home at midnight my parents had been waiting for nearly three hours.A. at that

问题补充：

I arrived home at midnight, my parents had been waiting for nearly three hours.

A. at that time

B. by that time

C. at which time

D. by which time

答案：

A. at that time

B. by that time

C. at which time

(答案→)D. by which time

解析：这题考查介词和非限制性定语从句，从句式结构看这是非限制性定语从句，又根据从句的时态：过去完成时，可以判断是by，所以填by which time。选D。句意是：我午夜到家，到那时为止我父母已经等了近3小时了。