题目

Sales of CDs have greatly increased since the early 1990s, when people ______ to enjoy the advantages of this new technology.     A. begin       B. began       C. have begun       D. had begun 答案：B 解析: 因when引导的是一个非限制性的定语从句，其先行词是1990s，指过去的一个时间，故应用过去式began.

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