【正确答案】 D

【答案解析】once是连词，作“一旦……(就……)”讲，用来引导时间或条件状语从句。例如：As long as a word remains unspoken，you are its master once you utter it ,you are its slave， 一句话在你没有说之前，你是它的主人；你一旦说出了口，你就是它的奴隶。Once the state has been founded，there can no longer be any heroes．They come on the scene only in uncivilized conditions． 国家一旦建立便不会再有英雄。他们是在尚未开化的背景下出现的。