Final answer:
The correct answer is option C. The harness in 'The Call of the Wild' represents Buck's obedience to serve John Thornton. Buck's willingness to be harnessed and his desire to do something great for Thornton underscore their strong bond.
Step-by-step explanation:
In Jack London's 'The Call of the Wild,' the harness is a symbol of Buck's obedience to serve John Thornton (Option C). When Buck willingly steps into his harness, he is not only accepting his role as a sled dog but also displaying his loyalty and dedication to Thornton.
This act of accepting the harness represents Buck's commitment to his master rather than his will to survive (Option A), his desire to return to the wild (Option B), or a lack of trust in mankind (Option D). The sense of duty and affection towards Thornton is strong enough to inspire Buck to want to perform a 'great thing' for him, showcasing the bond they share.