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. beginning

D. begun

答案：

A. begins

B. having begun

C. beginning

D. begun

解析：

可视为once it is begun之省略。