If the options are:
A. Buck's thoughts
B. Spitz's thoughts
C. Spitz's actions
D. Others' dialogue about Spitz
Then the correct answer, in my opinion, is C. Spitz's actions. Spitz is not a round character. We don't get to delve into his thoughts much, simply because he is an alpha dog whose only goal is to confirm his strength and authority through aggression. So, he fights Buck a few times, as well as any other dog that would threaten his position.