Robert is said abroad, but I do not know what country he studied in.A. to have studiedB. t

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(答案→)A. to have studied
B. to study
C. to be studying
D. to have been studying
解析：此题考查非谓语动词的用法。is said to do 结构中的不定式形式有三种，即：to do, to be doing，to have done, 并有相应的被动语态。做此题的关键是but从句中动词的时态，句中studied为过去时态，意味着他过去在国外学习，故用不定式的完成式，而选B则表示study动作是将要发生的，选C则表示动作是正在进行。