Read the literary analysis written by Cynthia about part 5 of The Call of the Wild. In The Call of the Wild, Buck is presented as an intensely loyal dog to those who earn his love and affection. Saved by Thornton from a brutal beating by Hal when he "was too near dead to be of further use in hauling the sled," Buck’s loyalty to Thornton first began. However, as described by London, it was more than just the fact that Thornton had saved his life that earned Thornton Buck’s adoration; it was also the fact that Thornton "was the ideal master." Even when Buck felt strongly the natural instincts that were calling from the wild, "the love for John Thornton drew him back to the fire again." Loyalty can be a powerful force.

How could the final sentence be revised to present a stronger conclusion?

Even loyalty is no match for the urges Buck feels to return to the wilderness.
Buck’s loyalty to Thornton is the only thing that keeps him alive in the Yukon.
Once forged, loyalty is a powerful opponent for even Buck’s natural instincts.
Loyalty is the only force in nature that allows Buck to deny the call of the wild.