Explanation

Reading the question: the question gives us a fact of introduction, a clause of evidence, and a clause of conclusion. We need to strengthen the conclusion. However, the easiest way to strengthen an argument is first to weaken it. The strengthener will patch a key area of weakness.

Creating a filter: since we are working with an argument, we can use term matching:



The key connection of this argument is in the second line. It's that behaviors specific to local populations must be cultural, not genetic. That is what makes or breaks this argument: the bond between "local population behavior" and "cultural rather than genetic factors." We'll look for these points in the answer choices.

Applying the filter: The promising choices are (B) and (E), both of which hit on the idea of "cultural, not genetic." Choice (A) doesn't touch on either key point, so it's out. Choice (C) talks about species, not populations, and if it's relevant to the cultural vs. genetic question at all, it would weigh in on the wrong side, for genetics. Choice (D) is neutral to the argument: a lack of contact doesn't help us differentiate between behaviors and genes, since both behaviors and genes are isolated in their own ways. Choice (E) concerns mating dances, and we have no evidence connecting mating dances and singing styles, so it doesn't strengthen the conclusion about singing styles. That leaves us with choice (B).

Logical proof: we can use the negation test to confirm choice (B). If younger cowbirds never interacted with their parents, or if they were born knowing how to sing, the argument would be greatly weakened: singing would appear to be genetically acquired. Therefore, the un-negated form of (B) is indeed a strengthener. The correct answer is (B).