Explanation
Correct answer: D.
Choice D is the best answer because it most accurately states the main idea of the text. After establishing that Buck views most people “as nothing,” the text explains that Buck won’t acknowledge people other than Thornton unless they appear friendly toward Thornton, and even then he’s only reluctantly accepting. Thus, the text focuses on the idea that Thornton has a special status in Buck’s mind, with Buck holding him in higher regard than other people.
Why the other choices are wrong
Choice A
Choice A is incorrect because the text conveys that Buck isn’t social with people other than Thornton but doesn’t address Buck’s life or temperament before he lived with Thornton.
Choice B
Choice B is incorrect because the text conveys that Buck doesn’t really care about people other than Thornton and is aloof toward them. However, there’s no indication that Buck mistrusts and avoids people generally; indeed, he accepts Thornton, who is a human.
Choice C
Choice C is incorrect because the text refers to random travelers praising and petting Buck and Thornton’s partners giving Buck favors, but there’s no indication that any of these people are Thornton’s friends or that they have a particular fondness for Buck.