题目内容
The research is so designed that once ______ nothing can be done to change it.
A. begins B. having begun C. beginning D. begun
D
once begun是once引导的条件状语从句的省略形式。= Once it is begun

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题目内容
The research is so designed that once ______ nothing can be done to change it.
A. begins B. having begun C. beginning D. begun
D
once begun是once引导的条件状语从句的省略形式。= Once it is begun
|