The Heating of the Interior of Io, the Innermost Galilean

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

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