This question asks you to infer what the author thinks about Drescher's ideas. The passage addresses Drescher's "idealization of British traditions of liberty" at line 31. Here, the author tells us that Eltis's ideas support the work of Williams, and run counter to those of Drescher. The author discusses Eltis's work approvingly. In contrast, the author does not seem to find Drescher's ideas to actually provide an answer (lines 20-28). So, you can infer that the author isn't too impressed with Drescher's ideas.
Answer (B) is correct because the author concludes that Drescher's argument leaves questions unanswered. He does not seem to believe Drescher's argument that the British would have become abolitionists when they were deeply divided by class struggles (lines 23-28). The author finds his views somewhat unrealistic.
Answer (E) is incorrect because the author never implies that he finds Drescher's views convincing, even superficially. Instead, the author raises questions about Drescher's work.