Columnist: The Hoopton municipal water treatment plant recently discovered a major problem with the adsorptive medium used in its treatment process. This medium helps remove iron and manganese from drinking water, but during the time that this part of the treatment process was not functional, residents suffered no adverse health effects. The insignificant outcome of this supposed disaster suggests that the presence of these minerals in drinking water is not as detrimental as watchdog groups would have us believe.

Which of the following, if true, would most seriously weaken the columnist's argument?

A) No residents have fallen ill in other municipalities with similar problems with their adsorptive media.

B) The potassium permanganate added in a later step in the treatment process removes most of the iron and manganese from the water supply.

C) Because the municipal treatment plant is so small, it was exempted from disinfection requirements after meeting certain strict criteria.

D) The Commission of Environmental Quality is responsible for ensuring that the treatment processes in all municipal facilities are fully operational.

E) Because it was summer, most residents of Hoopton were away on vacation when the malfunction occurred.

Source:Ready4GMAT

_________________

Hi,
Lets break Columnist's argument.
Premise 1: Some municipal dept RECENTLY discovered a MAJOR problem with the absorptive medium.
Premise 2: THIS medium HELPS removing X & Y. BUT(trigger point) while this medium was not being used, resident suffered NO adverse health effects.
Conclusion: Presence of X & Y in drinking water is not as detrimental as groups believed.

The reason I have typed adjectives in upper case is because one should lay emphasis on them while reading. Second, trigger word showed act as an alarm because a significant information is about to be revealed which could change the course of the argument.

We are asked to weaken the columnist's argument.

How can we do this?

We could either show that X & Y are serious components (attacking the conclusion) OR present a new information, which would act like a premise, weakening the argument.



May be their absorptive media was of good quality. Loser



This is a new information saying that X & Y are removed from water by an alternative solution at a later stage. So the supplied water does not contain X & Y. This weakens/invalidates the author's argument. Contender



Still does not do anything to weaken the author's argument. Loser



Still does not do anything to weaken the author's argument. Loser



This is a trap answer choice. Fewer people to drink infected water, fewer people falling ill than the original population. But still does not weaken the author's argument. Loser

So, B is the only valid answer choice that weakens the author's argument.
_________________