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

Q: Which group of the 1970's featured Tony Iommi on guitar, Geezer Butler on bass and Bill Ward on drums?

A: geezer butler
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Q: What is the name of the main thoroughfare in Barcelona, which runs from the Placa de Catalunya to the sea?

A: barcelona
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Q: Who choreographed the ballets Swan Lake and Don Quixote, among others?

A:
don quixote
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