How is Answer Choice B possible?

Thanks for your question, @HillaryMaria. This is an Error in Reasoning question, so the first thing we want to do is be sure we understand the flawed reasoning set forth in the stimulus. The stimulus can be diagrammed, as follows: Premise: HD-some-SUL [on some hot days, smog reaches unhealthy levels] Premise: HD-some-WFE [on some hot days, the wind blows in Sent from my iPad Conclusion: SUL-some-WFE [on some days when the wind blows in from the east, smog reaches unsafe levels] This conclusion does not follow from these premises. You cannot draw a transitive inference from two "some" statements. This is what answer choice (B) says, in classically convoluted LSAT language. Let's break it down to be sure we understand it. The argument "fails to recognize that one set" [hot days] may have some members in common with each of two others [(1) days when smog reaches unhealthy levels and (2) days when the wind blows in from the east], even though those two other sets have no members in common with each other. Precisely. There is no necessary overlap between SUL and WFE. Hope this helps! Please let us know if you have any additional questions.

Thank you very much!