19. When permits for the discharge of chemicals into a waterway are issued, they are issued in terms of the number of pounds each chemical that can be discharged into the waterway per day. These figures, calculated separately for each chemical for which a permit is issued, are based on an estimate of the effect of the dilution¹ of the chemical by the amount of water flowing through the waterway. The waterway is therefore protected against being adversely² affected³ by chemicals discharged under the permits.
The argument depends on the assumption that
(A) relatively⁴ harmless chemicals do not interact with each other in the water to form harmful compounds
(B) there is a swift flow of water in the waterway that ensures rapid dispersion of chemicals discharged
(C) those who receive the permits do not always discharge the entire quantity of chemicals that the permits allow
(D) the danger of chemical pollution of waterways is to be evaluated in terms of human health only and not in terms of the health of both human beings and wildlife
这个假设题目请大牛们重点讲解,A/B我的确是没有分开的我觉得两个都是假设.答案是A.
M: A是相关选项, 与原文中的separately对应, 如果取非,不同的chemical合成新的chemical, permit的作用就不存在了, 结论中的permits --> protection就不成立. 所以A是答案.
B的问题在于1. 和原文中的重点问题无关(见上) 2. 非必要条件,而是充分条件. 原文提到dilution, 所以chemical要被冲散,而不是聚集在某处. B是一个充分条件, 既:有A,就有dilution. 但是原文并没有提出B这种情况是唯一的办法. 既还有可能通过其它手段来解决dilution的问题.
举一个例子: 为了节约用电, 要求不开灯或不用电器. 如果节约了用电,我们不能推出一定是没开灯或一定是没用电器

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