challenge: What did Peter Goldreich's 1966 paper reveal about the orbits of moons in the Solar System?
  
  A. Moons closer to their planet have a constant orbital inclination with respect to the ecliptic
  B. Moons further away from their planet have a constant orbital inclination with respect to the planet's equator
  C. Moons closer to their planet have a constant orbital inclination with respect to the planet's equator, while those further away have a constant inclination with respect to the ecliptic
  D. The orbital inclination of moons is solely determined by the tidal influence of the Sun
  Answer: 