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：
试题分析：本题测试的是动词不定式在日常生活中的使用能力。此题最大的干扰项D．to have been studying来自动词时态的复杂烦琐的种种语法规则。如果平时时态教学从简，“顾名思义”地理解时态的最基本语法就在它的术语名称之中，那么 A．to have studied就是现在完成时态，因为上下文的Robert is said abroad，和but don’t know what country…都指“现在”，那么，下文的What country he studied in中的studied又说明动作是过去发生，其结果在现在，现在没有“正在进行”，故而现在完成进行时态的D．to have been studying不是最佳选项。
