If he occurs at length in this account, it is because he contributed much to the trip. A dog, particularly an exotic like Charley, is a bond between strangers.

The narrator says Charley appears at length because he contributed much to the trip. That means the amount of space devoted to him emphasizes his importance to the story, so the best answer is “The length of the description emphasizes his importance to the story.” The passage does mention that Charley is exotic, but it identifies his contribution to the trip as the reason for the extended account.

AI-written and checked against the verified answer.