— 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
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科目：高中英語 來源：0111 期中題 題型：單選題

— 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

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