Read the excerpt from The Call of the Wild. When Buck earned sixteen hundred dollars in five
minutes for John Thornton, he made it possible for his
master to pay off certain debts and to journey with his partners into the East after a fabled lost mine, the history of which was as old as the history of the country.

Where does this event fit in the plot's structure?

A. rising action
B. exposition
C. falling action
D. resolution