核心问题
上道试题明明写着 during the past fifty years(在过去的50年里)，为什么还要求谓语动词使用现在完成时（has become）呢？
词典解答
关于这个问题的详细解答，见 before(adv.)，in the past。
练习题
请做下面的英语试题：
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In ____, the advent of the telephone, radio, and television has made rapid long-distance communication possible. A. one hundred years later B. one hundred years ago C. the one hundred years since D. the last one hundred years (TOEFL)
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Industrial management is the aspect of business management that was most prominent in the United States for the past eighty years. (TOEFL)