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

Q: Physics. What is the SI unit for amount of substance?

A: amount of substance
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Q: 'Edward Lewis' and 'Vivian Ward' were the principal characters in which popular 1990 film?

A: edward lewis
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Q: William Lamb was the family name of which 19th century titled British Prime Minister?

A:
prime minister of the united kingdom
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