What Is the Cause of Its Many Volcanic/geyser-Like Eruptions on the Moon

What is the cause of its many volcanic/geyser-like eruptions on the moon Io?

A) its surface is at the triple point of methane, where it can be gas/liquid/solid
B) Jupiter's magnetic field causes huge bolts of lightning to hit Io and heat the surface
C) the gravitational stress of being so close to Jupiter and its other large moons heats the Io's inside
D) there is a metallic magnetic layer inside Io which is explosive
E) inhabitants of Io are intercepting Earth TV transmissions; it's making them throw up
Section 12.3: Titan and Triton