Why would the heavier material like metals and rocks be able to stay close to the center of the rotating disk?

The study of where things are 

Geothermic gradient is the rate of increasing temperature with respect to increasing the depth in the earths interior. away from tech tonic plates boundaries, it is about 25-40 c/km (72-87 degrees f/mi) of depth near the surface in most of the world.

Answer your driving test ;

The correct answer is a.