Answer:
B.Spitz is the antagonist because the others are rebelling against his leadership.
Explanation:
"The Call of the Wild" (1903) is a short adventure novel by Jack London set in Yukon Canada in 1890's. It narrates the story of a dog named "Buck". In earlier part of the story Buck lives in California USA, but is stolen and sold to work as a sled dog in Alaska. This excerpt is from this part of the story when Buck has to work in a team led by Spitz.
In this excerpt Spitz is the antagonist to Buck not only because other dogs rebel against Spitz and give Buck the lead rule, but also because Spitz becomes a coward and does not take action to take the leadership back from Buck.
Option A is not correct because starting a rebellion is not any criteria to establish one as an antagonist. More often (but not necessarily) an antagonist is bad-natured, coward, lacks leadership, so Buck should not be adjudged as an antagonist. The behavior of Billee also plays an important role in deciding who the antagonist and protagonist of the excerpt is. He is referred to as good-natured, but against Spitz, he is no more so. This shows Spitz had flaws which make him an antagonist. Billee's choosing Buck as leader shows that he (Buck) is a better leader and hence a protagonist.
Option C and D are incorrect because Dub's, Joe's, and Billee's behavior is not their's own, but encouraged by Buck, so they are neither antagonists nor protagonists.