Given a factoid/trivia type question, generate the topic of the question. The topic is the entity the question talks about.
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Question: Which actress played Arwen in the trilogy of films?

Answer: arwen


Question: Chris Martin is the lead singer with which band who had several hits in the 2000s?

Answer: chris martin


Question: Who leads The CBS Orchestra, the house band for The Late Show with David Letterman?

Answer:
cbs orchestra