This is a key event in The Call of the Wild.

Thornton knelt down by Buck’s side. He took his head in his two hands and rested cheek on cheek. He did not playfully shake him, as was his wont, or murmur soft love curses; but he whispered in his ear. “As you love me, Buck. As you love me,” was what he whispered. Buck whined with suppressed eagerness.

How does the event affect plot development?

AIt shows that Thornton and Buck are carefree and do not take things seriously.
BIt makes Buck appear to be a disobedient pet that Thornton cannot control.
CIt shows that Buck and Thornton have a true understanding of each other’s needs.
DIt makes Thornton and Buck appear to have a lack of trust for each other.

The best answer to the question: How does the event affect plot development, would be: C: It shows that Buck and Thornton have a true understanding of each other´s needs.

Explanation:

"The Call of the Wild" is a novel that was written by Jack London, and which was published in 1903. In this particular excerpt, which makes part of the events that take place in chapter 6 of the book, Buck, and Thornton are challenged to prove that Buck can pull a sled that has been overloaded with some really heavy products, several yards. Bets are made and the people of the town do not think such a feat is possible, regardless of how powerful Buck may look, as a sled dog. As the two of them get prepared, Thornton approaches Buck and says "As you love me, Buck. As you love me." The dog responds to the only master he has ever really loved, with a loving gesture of his own, and after this, starts to pull and manages to win the bet. The exchange between Thornton and Buck, and the success of their enterprise, show the connection between the two of them, and that is why C is the correct answer.