Which of the following best explains the motion represented by the arrows?
a. Rock is heated near the core at Point A, and therefore becomes less dense. It rises
towards Point B. As it moves from Point B to Point C, it is cooled and becomes denser,
so it sinks at Point D.
b. Rock is cooled near the core at Point A, and therefore becomes more dense. It rises
towards Point B. As it moves from Point B to Point C, it is heated and becomes less
dense, so it sinks at Point D.
c. Rock is heated near the core at Point A, and therefore becomes more dense. It rises
towards Point B. As it moves from Point B to Point C, it is cooled and becomes less
dense, so it sinks at Point D.
d. Rock is heated near the core at Point A, and therefore becomes less dense. It rises
towards Point B. As it moves from Point B to Point C, it is cooled and becomes less
dense, so it sinks at Point D.