—This returned Chinese scholar has become one of the top experts in this field.—Yes I kn

问题补充：

—This returned Chinese scholar has become one of the top experts in this field.

—Yes , I know him very well. He in Africa with wild animals for eight years.

A. has worked

B. had worked

C. worked

D. has been working

答案：

A. has worked

B. had worked

(答案→)C. worked

D. has been working

解析：考生极易受for eight years这一时间状语的干扰，从而选完成时。其实，只要仔细审题，就不难看出这是对一般过去事实的论述。故选C。