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

Q: In which war did the Sack of Badajoz takeplace?

A: siege of badajoz
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Q: Established in 1919, which is the world's oldest surviving airline?

A: airline
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Q: What was first demonstrated by Alexander Graham Bell at the Philadelphia Exhibition in 1876?

A:
alexander graham bell
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