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
relatively4 harmless chemicals do not interact with each other in the water to form harmful compounds
there is a swift flow of water in the waterway that ensures rapid dispersion of chemicals discharged
those who receive the permits do not always discharge the entire quantity of chemicals that the permits allow
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
这个假设题目请大神们重点解说,A/B我的确是没分开的我感觉两个都是假设.答案是A.
M: A是有关选项, 与原文中的separately对应, 假如取非,不一样的chemical合成新的chemical, permit有哪些用途就没有了, 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 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. 但原文并没提出B这样的情况是唯一的方法. 既还大概通过其它方法来解决dilution的问题.
举一个例子: 为了节省用电, 需要不开灯或不需要电器. 假如节省了用电,大家不可以推出肯定是没开灯或肯定是没用电器
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