◎ 题干
— This returned scientist has become one of the top experts in his field. 
— Yes, I know him very well. He once _____ in South America with wild animals for eight years.

A. has worked
B. worked
C. had worked
D. has been working
◎ 答案
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◎ 解析
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◎ 知识点
    根据n多题专家分析,试题“— This returned scientist has become one of the top experts in his field.— Yes, I know him very well. He once _____ in South America with wild animals for eigh…”主要考查了你对  【一般过去时】  等知识点的理解和应用能力。关于这些知识点的“档案”,你可以点击相应的链接进行查看和学习。