请教：大全-10-13

Exports of United States wood pulp will rise considerably during this year. The reason for the rise is that the falling value of the dollar will make it cheaper for paper manufacturers in Japan and Western Europe to buy American wood pulp than to get it from any other source.
Which of the following is an assumption made in drawing the conclusion above?
(A) Factory output of paper products in Japan and Western Europe will increase sharply during this year.
(B) The quality of the wood pulp produced in the United States would be adequate for the purposes of Japanese and Western European paper manufacturers.
(C) Paper manufacturers in Japan and Western Europe would prefer to use wood pulp produced in the United States if cost were not a factor.
(D) Demand for paper products made in Japan and Western Europe will not increase sharply during this year.
(E) Production of wood pulp by United States companies will not increase sharply during this year.

答案是B。可是C为什么不对呀？题意说dollar value下降使得日本和欧洲从美国进口纸浆更便宜。C说如果成本不是一个影响因素，日本和欧洲的造纸厂将宁愿使用美国产的纸浆。这难道不是个假设吗？如果把C取非：“如果成本不是一个影响因素，日本和欧洲的造纸厂将不愿使用美国产的纸浆”。不就是削弱吗？我的理解错在哪里呢？这道题我百思不得其解，请各位NN们指点指点迷津吧。万分感谢！