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]选D once begun 在句中作状语,once这里是连词.“一旦 . 【查看更多】
题目列表(包括答案和解析)
(NMET 2002)The research is so designed that once ________ nothing can be done to change it.
