问题补充:
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
答案:
(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。