The question asks, "the author mentions that “Byron’s literary craftsmanship is irregular†(lines 27-28) most probably in order to..."
(B) says, "dismiss craftsmanship as a standard by which to judge poets"
The problem with (B) is that the author believes that Byron is worthy of attention even if his craftsmanship is not the best, but this does not necessarily mean that the author is wholly dismissing craftsmanship. It's possible that the author could believe that craftsmanship is often a really good standard, but it's not the only standard by which to judge poets, so this is why we can get rid of (B).
(C) says, "offer another reason why Byron is not a “great†poet"
On these types of questions (role questions), it's always helpful to try to come up with a prediction for what the correct answer choice is generally going to say. Looking back at the passage, we see that the author mentions that "Byron's literary craftsmanship is irregular" where he is conceding the point that Byron's poetry isn't that "great," and this is given to us in lines 24-28. (C) matches this well, so it's the correct answer choice.
Hope this helps. Let us know if you have any other questions!
