请ＬＡＷＹＥＲ帮忙解决一下该问题

15. Sven: Trade unions are traditionally regarded by governments and economists as restraints of trade, working against the complete freedom of the economy, but I believe that unions are indispensable since they are often the worker’s only protection against exploitation.

Ravi: I don’t agree. The exploitation of the workers and their work is a normal part of ordinary trade just like the exploitation of natural or other material resources.

Sven and Ravi will not be able to resolve their disagreement logically unless they

(A) define a key term

(B) rely on the opinions of established authorities

(C) question an unproved premise

(D) present supporting data

(E) distinguish fact from opinion

如何分析？特别是区分A和C！请教LAWYER！ 谢谢！