is known to us all only the theory on practice can be practical.A. Which; baseB. Which;

问题补充：

is known to us all, only the theory on practice can be practical.

A. Which; base

B. Which; based

C. As; based

D. As; basing

答案：

A. Which; base

B. Which; based

(答案→)C. As; based

D. As; basing

解析：考察定语从句和固定搭配。本题第一空是非限制性定语从句，which引导的非限制性定语从句不能放在句首，as指代后面一句话的内容，在句中作主语。第二空是固定搭配be based on…以…为基础。使用了based on practice来修饰名词theory。句意：众所周知，只有以事实为基础的理论才是适用的。故C正确。