What Is the Mechanism That Generates the Variable Component of Ganymede's

Multiple Choice

What is the mechanism that generates the variable component of Ganymede's magnetic field?

A) variable electric currents in the conducting upper atmosphere of this moon
B) electric currents induced in the conducting ocean by Ganymede's motion through Jupiter's powerful magnetic field
C) spinning of the moon whose surface is electrically charged, which is equivalent to an electric current
D) spinning and permanently magnetized iron core within the liquid ocean