问题补充：
Robert is said abroad, but I don’t know what country he studied in.
A. to have studied
B. to study
C. to be studying
D. to have been studying
答案：
(答案→)A. to have studied
B. to study
C. to be studying
D. to have been studying
解析：由 studied 可知，他曾到国外留过学，“留学”这个动作已结束并发生在谓语动作(is said)之前，所以要用完成式。
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