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

Krist Novoselic and Dave Grohl were two thirds of which band, formed in Aberdeen (Washington State) whose albums include Bleach and In Utero?
dave grohl

Who directed the 2005 film 'Brokeback Mountain'?
brokeback mountain

Which British scientist discovered acetylene in 1836?
acetylene