Perrault and Francois were the 2 couriers for the French-Canadian government that became Buck's masters.
Answer: C) Perrault and Francois
Explanation
Francois as a courier taught Buck how to become a working dog.
Perrault and Francois are both experienced therefore they are both Buck's masters.
As masters, they got skills and other traits to train dogs respectfully.
Francois has an English accent.