B is the best answer. It gives the reader the context of the quote by stating the speaker and what is happening. It also has the quote which is more credible than just a word or two pulled out. Since it's just introducing this information, it also allows the writer of the essay to expand the idea with further explanation.
You should know who your audience will be
John Thornton and Buck's connection goes far beyond the working relationship that Buck had with Francois and Perrault. He respected those men for their understanding of dogs and of nature, but he had no great affection for them. John Thornton is "the ideal master," for he understands Buck without difficulty or confusion. Buck loves him because he shows his need for Buck, repeatedly demonstrating that Buck can help him in ways that others can't.
