The research is so designed that once nothing can be done to change it.A. beginsB. havi

问题补充：

The research is so designed that, once , nothing can be done to change it.

A. begins

B. having begun

C. begun

D. Beginning

答案：

A. begins

B. having begun

C. begun

(答案→)D. Beginning

解析：该题主要考查省略句的用法。译文：这项研究就这样定下了，一旦开始就无法改变。

句中once作“一旦……”讲，引导一个条件句，出于这个条件句的主语与主句的主语（the research）一致，所以省略掉了主语it和系动词is，只剩下一个过去分词begun，故最佳答案应选D。A项的错误在于缺少主语，B、D两项都是现在分词，不能用在条件句中作谓语，故可排除。