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    精英家教网 > 高中英语 > 题目详情

    The research is so designed that once _______ nothing can be done to change it.

    A. begins B. having begun  C. beginning  D. begun

    D


    解析:

    由于 the research 与 begin 是被动关系，故用过去分词 begun。Once begun 可视为 once it is begun 之省略。

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