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

答案及解析： A

解析：

解题思路：本题考查不定式完成时的用法，不定式完成时表示动作发生在谓语动词之前，提示在后半句，but I don't know what country he studied in，这说明他过去在国外留过学．