The Structure of Ganymede, a Galilean Satellite of Jupiter, Is

The structure of Ganymede, a Galilean satellite of Jupiter, is thought to be:

A) a thick crust of ice, a rocky mantle, and metallic core.
B) about half rock and half ice, with the rock at the center and the ice outside.
C) a large rocky core with a thin layer (100 km thick) of ice and water over it.
D) mostly or entirely rock with no firm evidence of an iron core, but with active volcanoes on its surface.