The main purpose of passage A is to present Ricks' disagreement with the point of view of Laura. For Passage B, it is mainly about the author disagreeing with certain points of Ricks. Thus answer choice B is correct.
A) "important idea" here should be refering to plagiarism. But neither passage is mainly tracing its historical development, but certain people's attitude about it.
C) shifting attitudes is slightly mentioned in B, but not at all in A
D) nothing dominant is mentioned
E) deeply problemetic is too strong for passage B