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

发布时间：2020-08-17 14:44:47

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
D. begun
解析：
可视为once it is begun之省略。
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