The reason he was late was he had taken a wrong bus.A. why; because B. for; becauseC. why;

问题补充：

The reason he was late was he had taken a wrong bus.

A. why; because

B. for; because

C. why; that

D. for; that

答案：

A. why; because

B. for; because

(答案→)C. why; that

D. for; that

解析：考查定语从句和表语从句。本题使用的是固定句型The reason why...is that...“......的原因是......”。从句he was late不缺成分，先行词是the reason，因此，定语从句用why引导，for不能引导定语从句，排除B、D；was后跟从句作表语，从句he had taken a wrong bus是主谓宾结构，不缺成分，用that只起引导作用，排除A；故选C。