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：考查时态。句意：我们知道实验结果不会太久。主句为一般将来时的句子中，从句用一般现在时表示将来的动作，故选C。
