The research is so designed that oncenothing can be done to change it. A. beginsB. having

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

A. beginsB. having begun C. beginning(答案→)D. begun解析：该题题干的意思应为“研究工作计划得如此周密,一旦工作开始,什么事情也改变不了它”?当once (或when, while, if, as if, though/although, as, until, until, whether, unless, since等)引导状语从句时,若从句中的主语与主句中的主语相同(或从句中的主语为it), 且从句的谓语中有be时,可省略从句中的主语和be, 而只保留形容词?分词?动词不定式?介词短语等,故答案为D?

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