Why Does the Innermost Galilean Satellite of Jupiter, Io, Not

Why does the innermost Galilean satellite of Jupiter, Io, not show a cratered surface, as expected from the appearance of equivalent-sized objects like the Moon, Mercury, and Mars?

A) The large gravitational force generated by Jupiter has diverted most objects away from Io.
B) The surface is completely covered by an ocean of water, partly frozen into ice, which will obviously not show craters.
C) Volcanic action recoats the surface regularly and continuously.
D) Dust storms triggered by heating from Jupiter have quickly filled in any craters.