----This returned Chinese scholar has bee one of the top experts in this field.
----Yes,I know him very well.He in Africa with animals for eight years.
A. has worke
B. had worked
C. worked
D. has been working
网友回答
A. has worke
B. had worked
(答案→)C. worked
D. has been working
解析：since，for作为连词，引导时间状语（从句）如果谓语动词是延续性的一般过去时，其表达的含义是从这个动作结束以来，恰好和动词的词义相反，具有否定的含义；如果谓语动词是非延续性的一般过去时，其表达的含义是从这个动作开始以来，恰好和动词的词义一致，具有肯定的含义
It is 3 years since her husband worked as a news journalist. 她丈夫不当记者已三年了。
It is 5 years since I joined the army. 我在部队已服役五年了。（仍在军队服役）