B v D

Additionally, is it relevant at all that the conclusion does not say rainwater and simply says water?

Hi Jwebb, thanks for the question! B is saying that the statement is evidence that rainwater runoff is a more serious issue than pollution from industrial discharge. There are two issues with this statement. Firstly, the stimulus only speaks about water pollution, and B make a blanket statement about rainwater runoff being a more serious issue in general. Secondly, we do not know that just because it contributes to more water pollution that it is a more serious problem. Perhaps a given amount of chemical waste from industrial discharge is more harmful than even 10x the amount of rainwater runoff. D is accurate. It says that it is a premise for the conclusion. Which it is. As for the issue of the conclusion saying water rather than rainwater, I see how this can often be an issue when they switch terms. But in this case, rainwater is water nonetheless. Hope this helps!