答案：D

题目分析：如果将题干改成下列句子：It is said that Xiao Li  _______ abroad, but I don’t know what country he studied in.上下句谓语动词发生的时间关系就一目了然：很显然“留学”应该发生在过去。It is said that Xiao Li studied abroad, but I don’t know what country he studied in.转换成：Xiao Li is said to have studied abroad, but I don’t know what country he studied in.动词不定式的完成式除了表示“完成(Xiao Li is said to have gone abroad.据说小李已经到国外去了)”，还可以表示“过去”。如果将下文改成“but I don’t know what country he is studying in”则备选项B就是正确答案了。

句意：据说小王在国外留过学，但是我不知道他在什么国家学习过。