The reserch is so designed that once ___ nothing can be done to change it.A.begins B.having begun C.beginning D.begun 为什么选D?

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Thereserchissodesignedthatonce___nothingcanbedonetochangeit.A.beginsB.havingbegunC.beginningD.begun为

The reserch is so designed that once ___ nothing can be done to change it.A.begins B.having begun C.beginning D.begun 为什么选D?
The reserch is so designed that once ___ nothing can be done to change it.
A.begins B.having begun C.beginning D.begun
为什么选D?

The reserch is so designed that once ___ nothing can be done to change it.A.begins B.having begun C.beginning D.begun 为什么选D?
research 被动begin:that once (省略了the research is) begun nothing can be done to change it.

begun (having been begun) 形容 the research

从句是过去时 所以要用begun 这个过去式

一般过去时表被动,一旦开始就无法改变。