采用实验调查方法，必须（）。

A.测试调查效果

B.控制市场因素

C.正确控制无关变量影响

D.寻找科学实验场所

— Why don't we choose that road to save time
— The bridge to it（）.

A. has repaired

B. is repaired

C. is being repaired

D. will be repaired