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: Who composed Air on the G String?

Answer: air on the g string


Question: Which form of dementia is named after a German psychiatrist who first described it in 1906?

Answer: dementia


Question: Which novel, first published in the UK in 1921, was the first to feature Agatha Christie's detective, Hercule Poirot?

Answer:
christie