The research is so designed that once nothing can be done to change it.A. beginsB. having

发布时间：2020-08-17 11:57:27

The research is so designed that once      nothing can be done to change it.
A. begins
B. having begun
C. beginning
D. begun

网友回答

A. begins
B. having begun
C. beginning
(答案→)D. begun
解析：答案选D，可视为once it is begun之省略。
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