The research is so designed that once nothing can be done to change it.
A. begins
B. having begun
C. beginning
D. begun
网友回答
A. begins
B. having begun
C. beginning
(答案→)D. begun
解析：
D。由于 the research 与 begin 是被动关系，故用过去分词 begun。Once begun 可视为 once it is begun 之省略。