It long before we the result of the experimentA. will not be；will knowB. is；will knowC. w

问题补充：

It long before we the result of the experiment．

A. will not be；will know

B. is；will know

C. will not be；know

D. is; know

答案：

A. will not be；will know

B. is；will know

(答案→)C. will not be；know

D. is; know

解析：考查固定句型。It be 一段时间 before从句。意为：一段时间以后某事才发生。Before从句里用一般现在时代替将来时，主句用将来时。故C正确。