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: In which city was Christopher Columbus born?

Answer: columbus


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

Answer: chris martin


Question: Who wrote the short story on which the 2006 film 'Brokeback Mountain was based?

Answer:
brokeback mountain