Robert is said abroad but I don’t know what country he studied in. A. to have studiedB.

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。