Every year many people become ill because of airborne mold spores in

Hey All,

Even though the right answer was eventually arrived at here, there was enough confusion I thought it might be worth outlining. Let's do it.

Every year many people become ill because of airborne mold spores in their homes. After someone becomes ill, specialists are often hired to eradicate the mold. These specialists look in damp areas of the house, since mold is almost always found in places where there is substantial moisture. If one wishes to avoid mold poisoning, then, one should make sure to keep all internal plumbing in good condition to prevent leakage that could serve as a breeding ground for mold.

Conclusion: To avoid mold poisoning, keep plumbing in good condition.
Premises: Specialists check in damp areas of the house/mold is almost always in moist places
Assumption: Plumbing is the only thing that causes moisture.

Now I swear on a stack of bibles I wrote this assumption before looking at the answer choices. Think about it. The argument is airtight, other than this little issue. The conclusion involves plumbing, but that seems pretty specific, doesn't it? What about fixing the roof, so rain water can't get in? Truth is, there are plenty of ways moisture could get into the house.

As for a pattern, this is an eliminate alternate cause question. These are very common on the GMAT CR section, and there's a great thing to know about them: very often, when the question posits that A causes B, the assumption is that B doesn't cause A. It's called a causation/correlation mistake (we see two things happening, for example moisture and mold, and assume that moisture causes mold). Though sometimes the answer will just be any other old cause (like the leaky roof I suggested), very often it's just a reversal (mold might cause moisture). Be on the lookout!

1]Mold itself does not create moisture.
ANSWER: Uh-oh. Think about it. If mold DID create moisture, then it wouldn't be enough to check the plumbing, because the mold could be anywhere. This would explain why it's always found in moist places.

2]Most homeowners know enough about plumbing to determine whether theirs is in good condition.
PROBLEM: This is a tricky one. If the conclusion were, "Homeowners should thus have no problem finding mold on their own," this would be the assumption. But the conclusion is that plumbing needs to be kept in good condition. If you don't know, you'd just have to learn.

3]Mold cannot grow in dry areas.
PROBLEM: We don't need to assume this, because the conclusion is not that all mold will be eradicated if plumbing is checked. It's only that if one wishes to avoid mold, one should keep plumbing in check. Even if mold can grow in dry places, the facts point towards moisture being the most common place to find it, and thus the conclusion would still hold.

4]No varieties of mold are harmless.
PROBLEM: Not the issue. Even if some are harmless, some aren't.

5]Mold spores cannot be filtered from the air.
PROBLEM: This might suggest another way that mold poisoning can be avoided (some type of filtration system), but as the conclusion relates to actually getting rid of the mold where it comes from, this answer choice is out of scope.

Hope that helps!

-t