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  • 更新 2022-09-03
  • 科目 英语
  • 题型 单选题
  • 难度 中等
  • 浏览 804

____ several times, the young scientist still kept on doing his experiments.

A.Having failed B.Having been failed C.Failed D.To fail
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相关知识点

severaltimes,theyoungscientist