Robert is said abroad, but I don’t know which country he studied in.
A. to have studied
B. to study
C. to be studying
D. to have been studying
网友回答
(答案→)A. to have studied
B. to study
C. to be studying
D. to have been studying
解析： study这一动作发生在主句谓语之前，所以用不定式的完成时；且but I don’t know which country he studied in.说明他已经不在国外学习了，所以选A。