For questions 1-3 choose the appropriate moon from this list:
A. Titan
B. Io
C. Europa
D. Enceldus
1) Most volcanically active moon in the solar system.
2) Jupiter Moon that is believed to have a large subsurface ocean?
3) Has cryovolcanoes that eject water ice into Saturn's E Ring?
4) All of the moons in the above list should have cooled long ago, what provides the internal heat source that allows some of these moons to be geologically active and/or have subsurface oceans?