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

Q: Who played the character Gene Hunt in the UK TV series 'Life on Mars' and 'Ashes to Ashes'?

A: life on mars
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Q: Aragon and Castile joined to form which country?

A: aragon
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Q: Berlin stands on which river?

A:
berlin
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