2. 外语
  3. __________(在1世纪末就开始投入使用), this kind of energy had brought great convenience for human beings.

__________(在1世纪末就开始投入使用), this kind of energy had brought great convenience for human beings.

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问题 __________(在1世纪末就开始投入使用), this kind of energy had brought great convenience for human beings.
选项
答案Having come into use at the end of 18th century
解析 考查分词作状语从句的表达。看整句时态，完全是描述过去的事情，所以要用分词的完成式having done的形式。“投人使用”译为come into use。
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大学英语四级

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