Which Mechanism Is MOST Likely to Have Taken Place While

Which mechanism is MOST likely to have taken place while Earth was molten to form the present structure of Earth?

A) All materials were thoroughly mixed by convection in the molten state, and Earth remained mixed as it cooled.
B) Hydrogen and helium became highly compressed by gravity and sank to the core below a layer of heavier rocky material.
C) Lighter elements sank to the center, leaving the heavier material to form the rocky surface as cooling proceeded.
D) Heavy elements sank to the center under gravity while lighter materials rose to the surface and solidified into rocks.