Bunuel
A certain type of mold known to cause a skin rash was discovered in the air-conditioning system of an office building where the workers had been complaining of this skin rash. The company hired to eliminate the mold cleaned out the entire air-conditioning system with a spray that was scientifically proven to kill this type of mold within 30 days. Therefore, any worker's skin rash appearing more than 30 days after the air-conditioning system had been cleaned could not have been caused by this particular mold.
Which of the following, if true, most seriously weakens the conclusion above?
A.The skin rash caused by the mold resembles rashes caused by common allergies.
B. Excessive moisture buildup in the AC system, which was the primary cause of the mold, was subsequently eliminated by repairs to the system.
C. The spray used to eliminate the mold is not effective against all types of organisms that may grow in AC systems.
D. The mold found in the building's AC system can survive and breed in many parts of the building, including the carpeting.
E. In buildings whose AC systems are infested with this mold, some individuals do not develop skin rashes.
Official Explanation
The words "most seriously weakens" indicate that this is a Weaken question. The correct answer will make it less likely that the conclusion follows from the stated evidence.
The conclusion is that skin rashes that developed more than 30 days after the AC system was cleaned for mold could not have been caused by the mold. The evidence offered is the fact that the AC was cleaned with a spray that kills this mold within 30 days.
The argument is assuming that the workers could not have been exposed to the mold through any other means besides the AC system. The correct choice will attack the argument's assumption. It will suggest some way that a worker could be exposed to the mold besides the air coming through the AC system.
(D) suggests a way a worker could be exposed to the mold and get a rash, even though the AC was cleaned. The mold could breed in other places besides the AC system.
(D) is therefore correct.(A) merely suggests that one may not be able to diagnose the cause of a rash just from its appearance. But this does not suggest some way that someone with a rash could have gotten it from the mold after the AC was cleaned. (A) does not, therefore, weaken the conclusion of the argument.
(B) may make it less likely that mold will grow back in the AC system. But this doesn't suggest how a skin rash appearing more than 30 days after the AC system was cleaned could be caused by the mold. (B) is not a weakener.
(C) is irrelevant, because the argument is only concerned with the mold and rashes it causes. Other organisms have nothing to do with this.
(E) points out that not everyone develops the skin rash. But the argument is not about those who don't get the skin rash--it's about those who do. Can the rash be caused by the mold, even more than 30 days after the AC system is cleaned? (E) doesn't speak to this and is therefore irrelevant to the argument.