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: In which Shakespeare play do the characters Ajax, Achilles and Ulysses appear?

Answer: achilles

Question: After Harold McMillan who was Britain's next Prime Minister?

Answer: britain

Question: In 1469, the crowns of the kingdoms of Castile and Aragon were united by the marriage of Isabella and Ferdinand. This was an important event in the history of which country?

Answer:
aragon