Which Best Exemplifies Acceleration

Which best exemplifies acceleration?

A) Rose, a six-year-old, is in a third grade class because she has mastered first and second grade subject content.
B) Carter is given more difficult reading material than her classmates in fourth grade.
C) Coralee, who has mastered the third grade science curriculum, teaches it to others in her class who have not.
D) Desmond studies subject areas not offered at his school, such as comparative religion and quantum physics.