Jack wishes that he ________ business instead of history when he was in university．A. studiedB. studyC. had been studyingD. had studied

步骤 1：理解句子结构
句子的主句是 "Jack wishes that he ________ business instead of history when he was in university."，其中 "wishes that" 引导一个虚拟语气的从句，表示与过去事实相反的愿望。
步骤 2：确定虚拟语气的时态
由于 "when he was in university" 表示的是过去的时间，因此从句中应该使用过去完成时，即 "had + 过去分词" 的形式。
步骤 3：选择正确的选项
根据上述分析，选项中只有 "had studied" 符合过去完成时的结构。