Answer: C - “The students who would end up the best in their class began to practice more than everyone else: six hours a week by age nine, eight hours a week by age twelve, sixteen hours a week by age fourteen, and up and up…”
Explanation: The excerpt states exactly what you're meant to prove. "The student who would end up the best in their class began to practice more than everyone else." This shows due to their hard work and long hours of practice, they were the most successful out of everyone in their class.