请教一道英语题！请详细解答，谢谢！

来源：百度知道 编辑：UC知道 时间：2024/07/04 07:08:29
The research is so designed that once _______ nothing can be done to change it.
A. begins B. having begun
C. beginning D. begun

D 等于 The research is so designed that once it is begun nothing can be done to change it.

once表示一旦怎么样就.... once在这里用法等于when，作为从句的引导词，所以作为修饰性从句的主语谓语（it is)可以省略。

你也许以后会遇到这样的考法: Once ____, the research can not be changed by anything. 也是填begun. 道理是完全一样的。

D
考察非谓语动词,被动的就是D了