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: The Byzantine Empire is the term used since the 19th century to describe the Roman Empire of the Middle Ages, centred on its capital, where?

Answer: byzantine empire

Question: What is the country of origin of the cheese called caerphilly?

Answer: caerphilly cheese

Question: Which 1942 film features the line Play it Sam, play 'As time goes by'?

Answer:
sam