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  • 更新 2022-09-03
  • 科目 英语
  • 题型 单选题
  • 难度 较易
  • 浏览 1136

I can still remember that it is since the 1990’s, _____ we began to use cell phones,_______ the number of mobile users has greatly increased.

A.while; when B.when; what C.before; that D.when; that
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Icanstillrememberthatitissince