Answer B

When the author states that "One can, if one wants, define genres of fiction as sets of texts sharing certain thematic similarities," it seems that the author is saying that readers expectations need not be considered in defining a genre. Although the author argues that a better way to classify genres is by relying on reader expectations, the author explicitly states that this is not the only valid way to demarcate genres and in doing so implies that reader expectations are nonessential (of course, depending on the method by which one classifies genres). (After all, thematic similarities as a method can exist independent of reader expectations.) I'm having trouble reconciling this fact with answer choice B being incorrect.