Step-by-step explanation:
The statement that best describes how Buck differs from the other dogs in this excerpt is: "Buck is more hardworking and determined to travel."
The excerpt mentions that all the dogs had to travel 1800 miles and were very tired, but Buck stood it and kept his mates up to their work, maintaining discipline. This implies that Buck is more hardworking and determined than the other dogs. Billee cries and whimpers regularly, Joe is sourer than ever, and Sol-leks is unapproachable. None of these behaviors suggest that these dogs are more hardworking or determined than Buck.