Hi mkarimi73!
For this one, we're asked to compare the passages and identify a common purpose to both. To understand why (C) is wrong, let's compare answer choice (C) and (B):
(B) to find fault with a way of approaching a scholarly topic
(C) to examine shifting scholarly attitudes toward a particular topic
For answer choice (C), in my reading it is hard to see which specific scholarly attitudes are "shifting," or what this might mean. There are scholarly attitudes mentioned in both passages to be sure, but I don't see anything about them shifting. Something like that might look, for example, like discussing trends in scholarship over time--that would make sense as "shifting scholarly attitudes," but there isn't material like that in this passage. In addition, even if one could identify a place where shifting scholarly attitudes is mentioned, this would need to be common to both passages given the question stem.
It's possible that the mention of postmodernism might have made mention of shifting scholarly attitudes to be appealing. In addition, postmodernism is mentioned in both passages. In the end, however, postmodernism doesn't seem to be discussed within a context of a shift in scholarly attitudes (there's no discussion of what came before or after it, for example).
Answer choice (B), like (C), mentions "scholarly," but does better at describing specific similarities between the two passages. They are both discussing the history of plagiarism. The blurb at the start of the passages seems important to note in terms of how they related to one another: "Passage A is adapted from an essay by historian Christopher Ricks; passage B is from the introduction, by historian Paulina Kewes, to a book in which Ricks’s essay appears." Passage A involves Ricks providing criticism of a scholar's book on the history of plagiarism. Passage B involves Kewes summarizing Ricks and also criticizing Ricks in the second half of the final paragraph. So both passages are criticizing a scholarly approach.