The Heating of the Interior of Io, the Innermost Galilean

Multiple Choice

The heating of the interior of Io, the innermost Galilean moon of Jupiter, is caused by

A) thermal heating from Jupiter because Jupiter emits more infrared radiation than it receives from the Sun.
B) continual bombardment by meteoroids attracted by Jupiter's enormous gravitational pull.
C) continuous tidal distortion by Jupiter and the other moons.
D) the fact that Io moves inside Jupiter's magnetosphere, where the temperature is as high as anywhere in the solar system.