Even Though Jupiter's Moon Io Is Similar in Size to Our

Even though Jupiter's moon Io is similar in size to our geologically dead Moon, it is more geologically active than the Earth. How can this be?

A) because Io orbits very close to Jupiter, it still has a lot of heat trapped inside from its formation
B) Io is tidally heated by tidal forces exerted by the outer Galilean moons, which flex and distort its interior
C) Io has much more radioactive decay occurring inside it than does the Earth
D) Io is tidally heated due to its elliptical orbit, which causes the large tidal forces exerted by Jupiter to constantly change, flexing and distorting its interior