◎ 题干
The research is so designed that once ______ nothing can be done to change it.
[     ]
A. begins
B. having begun
C. beginning
D. begun
◎ 答案
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◎ 解析
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◎ 知识点
    根据n多题专家分析,试题“The research is so designed that once ______ nothing can be done to change it. [ ]A. begins B. having begun C. beginning D. begun …”主要考查了你对  【过去分词】  等知识点的理解和应用能力。关于这些知识点的“档案”,你可以点击相应的链接进行查看和学习。