Given a factoid/trivia type question, generate the topic of the question. The topic is the entity the question talks about.

What was the first Apollo mission to leave Earth orbit and orbit the moon, in 1968?
apollo

Baltusrol Course lies in which US state?
baltusrol golf club

What system, available on the internet, was founded by Mark Zuckerberg, Eduardo Saverin, Dustin Moskovitz and Chris Hughes?
chris hughes