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: What is the SI unit of capacitance?

Answer: capacitance


Question: Which analgesic drug, first isolated in 1804, was named after the Greek god of dreams ?

Answer: analgesic


Question: The Lion, The Witch and the Wardrobe, a 2005 film based on the novel by C. S. Lewis, is set mainly in which land?

Answer:
c. s. lewis