Given an trivia question precisely answer the question with a word/phrase/name. External resources such as Wikipedia could be used to obtain the facts.
--------
Question: Emerald and aquamarine are varieties of which gemstone?

Answer: beryl


Question: Which painter is known as The Father of Impressionism?

Answer: claude monet


Question: Three of the Galilean moons of Jupiter are Io, Europa and Callisto. Which is the fourth?

Answer:
ganymede