Read this excerpt from The Call of the Wild. Since the beginning of the winter they had travelled eighteen hundred miles, dragging sleds the whole weary distance; and eighteen hundred miles will tell upon life of the toughest. Buck stood it, keeping his mates up to their work and maintaining discipline, though he, too, was very tired. Billee cried and whimpered regularly in his sleep each night. Joe was sourer than ever, and Sol-leks was unapproachable, blind side or other side.

Which statement best describes how Buck differs from the other dogs in this excerpt?

A. Buck is more sensitive of the needs of others.
B. Buck is better at pulling the sled over long distances.
C. Buck is more hardworking and determined to travel.
D. Buck is better at handling the strain of traveling long distances.