By the time he realizes the mistake he it will be too late for him to do anything about i

问题补充：

By the time he realizes the mistake he ，it will be too late for him to do anything about it.

A. has made

B. made

C. makes

D. will make

答案：

(答案→)A. has made

B. made

C. makes

D. will make

解析：考查时态by + 现在的时间，主句用现在完成时。