问题
选择题
The research is so designed that once _______ nothing can be done to change it.
A．begins
B．having begun
C．beginning
D．begun
答案
答案：D
“连词+分词”作状语，依然由句子主语与分词的关系来确定，主动关系用现在分词，被动关系用过去分词。the research 与 begin 是被动关系，用过去分词 begun。