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The research is so designed that once nothing can be done to change it. A. begins B. having begun C. beginning D. begun [解析]選D once begun 在句中作狀語,once這里是連詞.“一旦 . 【查看更多】

 

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(NMET 2002)The research is so designed that once ________ nothing can be done to change it.

[　　]

A．begins
B．having begun
C．beginning
D．begun

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