When permits for the discharge of chemicals into a waterway are issued, they are issued in terms of the number of pou...

shunhe on July 21, 2020

Hi @mikeheath,

Thanks for the question! So let’s recap the stimulus. We’re told here that when permits for putting chemicals in waterways are given out, they’re issued in terms of number of pounds of chemicals per day you can discharge. And these figures are calculated separately for each chemical, and calculated based on the effect of how much the chemical will be diluted by the water flow. The argument concludes that this practice protects the waterway against being adversely affected by chemicals discharged.

So now we’re asked for an assumption this argument depends on; in other words, this is a strengthen with necessary premise question. Now let’s take a look at (B). Does the argument have to assume that there’s a swift flow of water in the waterway that ensures rapid dispersion of chemicals discharged? No, not at all. Remember that we’re told in the stimulus that the permits account for the amount of water flowing through the waterway. So if water flows through more slowly (less water flows through), that fact would be accounted for in the permit. So the argument doesn’t need to assume that the water is swift. It could be slow, or in between. The argument would still hold, and so by negating (B) in that way (if there isn’t a swift flow of water, but another speed), and showing that the argument still holds, we’ve shown that (B) isn’t a necessary assumption, and so isn’t the right answer choice.

Hope this helps! Feel free to ask any other questions that you might have.