Without facts we cannot form a worthwhile opinion for we need to have a factual knowledge

问题补充：

Without facts, we cannot form a worthwhile opinion for we need to have a factual knowledge our thinking.

A. which to base on

B. which to be based on

C. on which to be based

D. on which to base

答案：

A. which to base on

B. which to be based on

C. on which to be based

(答案→)D. on which to base

解析：考查定语从句：句意为:没有事实，我们就不能形成有价值的观点，因为我们的思考必须以真实的知识为基础。upon which to base our thinking是动词不定式短语作定语，该短语中介词必须放在which前。 答案是D