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: Which film was based on the story The Sentinel by Arthur C Clarke?

Answer: arthur c. clarke

Question: Who composed 'Eine Kleine Nachtmusik' in the 18th Century?

Answer: eine kleine nachtmusik

Question: Which, chronologically, is the first of the Chronicles of Narnia, although it was the sixth of the series of books written by author C. S. Lewis?

Answer:
the chronicles of narnia