----This returned Chinese scholar has become one of the top experts in this field.----Yes,

----This returned Chinese scholar has become 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

A. has workeB. had worked(答案→)C. workedD. 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）

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