Explanation
A. This describes a mistaken reversal of the first sentence, which is not the error we are looking for.
B. (Correct Response) Presuming that gnats are necessary condition of wet conditions is the error. This is a way of stating the mistaken negation. Although it is a little bit camouflaged because it is stated in the contrapositive form, it becomes clear with a diagram.
Sentence 2: Gnat >> Wet climate (Here’s our rule, simplified)
Sentence 4: No gnats >> Not a wet climate (Here’s the fallacy of the inverse)
Option B: Wet climate >> Gnats (This is clearly reversed and negated, making it the contrapositive and therefore logically identical to the flaw described in the general explanation)
C. This is not the type of thinking we want on a question like this, we are given rules and asked to apply them. We know that gnats can ONLY survive in wet climates. That means all gnats, don’t fight the premises.
D. Out of scope, we do not care about what geckos eat, especially if those things are not gnats.
E. “Fails to establish” means that this is a required component of the argument. The argument does not require this additional clause. It also fights the premises because there are no gnats in dry climates, only wet ones.
Probably best to find the flaw before dealing with responses on this question because the flaw is very common, but the way it’s phrased in choice B is somewhat camouflaged. It is easier to find if we already know what we are looking for.