Thank you for your question. This is argument structure question, asking us to evaluate the role or function played by a particular portion of the stimulus. So, before we turn to the answer choices, let's be sure we are clear on exactly what is happening in the stimulus itself.
First, this is an argument. The conclusion of the argument is that it is misguided to argue that expressing true propositions contributes to the aesthetic merit of a poem.
What support is offered for this conclusion?
Premise: Most of the commonplace beliefs of most people are true.
Premise: The basis of poetic excellence, whatever it is, must certainly be rare (i.e., not commonplace).
Looking at the question stem, we see that the LSAT writers wish for us to identify the role or function of this second premise. That is answer choice (B).
We can eliminate answer choice (A) because the language in question is not the conclusion. Likewise, answer choice (C) can be eliminated because the language in question is not the sole premise offered in support of this argument's conclusion.
We can eliminate answer choice (D) because the phrase in question is not just background information. If the basis of poetic excellence must be rare, rather than commonplace, that, taken in tandem with the premise that most of the commonplace beliefs of most people are true, supports the argument's main conclusion that it is misguided to argue that expressing true propositions contributes to the aesthetic merit of a poem.
Answer choice (E) has it backwards. The phrasing in question is not itself being explained or bolstered by the argument overall.
Hope this helps. Let us know if you have any additional questions.
