Practice problem
(http://www.express.co.uk/news/nature/579195/WATCH-LIVE-Stargazers-to-get-best-ever-views-of-Saturn-s-rings)
What is the composition of Saturn's rings?
Mostly ice with some rocky bodies
Mostly hydrogen with some ice
Mostly rocky bodies with some ice
Mostly helium with some rocky bodies
Type a concept, like “slope” or “photosynthesis”.