#21 - Several years ago, as a measure to reduce the

[maximbasu]

Hello,
I chose B as the correct answer while the correct answer was A.

I understand B brings in new extraneous information. But how is A correct? I reasoned A was an opposite answer, because its focusing on moths that are unaffected--but the stimulus talks about months that are killed by the fungus.

Thank you, Maxim.

[Adam Tyson]

I see A as an example of eliminating an alternate cause, which could be anything other than the fungus that might have affected ALL gypsy moths instead of just the ones that are sensitive to the fungus. Gypsy moths overall have decreased, but gypsy moths not affected by the fungus (let's call these the immune moths) are now a larger percentage of all gypsy moths, suggesting that whatever reduced the gypsy moth population did not affect them (or affected them less). The correlation between fungus immunity and not decreasing strengthens (but doesn't prove) that the fungus is the cause of the overall decline.

Imagine you wanted to attack this argument - you might say that the reason the population decreased was that a predator of gypsy moths had become more prominent, or that a source of food for gypsy moths had become less abundant. Alternate causes, right? But those would likely have affected moths without regard to whether they were immune to the fungus or sensitive to it. Since the immune moths did not apparently decline, or at least declined less, that makes those alternate causes less likely, strengthening the original causal claim.

A true opposite answer is not one that focuses on the wrong thing, but one that has the opposite effect from what you needed. Here, an answer that suggested an alternate cause - like answer D - would be an opposite answer, because it would weaken rather than strengthen the argument.

[PositiveThinker]

This was a simple question that i just over thought. ugh.

[adlindsey]

I chose B on a review. I see why A could be right. But B also looks right, since it says it poisonous to few insects other than the gypsy moth; hence it WAS poisonous to the moth. In strengthen questions, the help can vary between 1%-100%. And B is in the lower spectrum

[Dave Killoran]

Hi A,

Careful here, because don't we already know that the fungus was poisonous to gypsy moths? The stimulus says, "a species of fungus that is poisonous to gypsy moth caterpillars." So, in (B), just knowing that it's poisonous to gypsy moths isn't anything new or helpful, and as such that doesn't in fact strengthen the argument.

Thanks!

[Laylalayla]

Hi Powerscore or anyone,

I'm having difficulty understanding why A is correct despite a previous awesome explanation given by Powerscore.

This is a Strengthen Q. Correlation /causation.

Answer A, is selected, but, my misunderstanding here is, I see A as an opposite answer of the conclusion. The conclusion states declines moths. Answer A) states increases moths. I'm so confused. Please advise what I'm missing here. Shouldnt I strengthen their conclusion? Meaning look for an answer that strengthens their declining point.

Is this because, I'm suppose to attack their conclusion? So how does that strengthen the conclusion?

Please help, thanks!!

[Rachael Wilkenfeld]

Hi Layla,

Answer choice (A) strengthens the conclusion by eliminating a possible alternative cause for the decrease in gypsy moths.

Here are the key facts from the stimulus
1. Entomologists introduced fungus poisonous to gypsy moths to oak trees (a key food source for them)
2. Since then there are fewer caterpillar and adult moths

Our conclusion tries to link those two facts into a causal conclusion--the fungus caused the decrease in these bugs. But we don't really have any reason to support that linkage. Correlation is not the same as causation.

Answer choice (A) helps us out by linking the fungus to fewer moths. It says that without the cause (poison fungus) we don't have the effect (fewer moths). That supports the causal conclusion that the fungus is what is causing the decrease in moth population. Also note that answer choice (A) is not contradicting the facts in the stimulus. It's not saying the overall population of moths increased. It's saying that a specific subset of moths, who aren't impacted by the fungus, increased in percentage of the gypsy moth population. We don't even know if those moths increased in number at all, just that their share of the gypsy moth population increased.

Hope that helps!