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 main river of Brazil?

Answer: brazil

Question: Which British Prime Minister signed the 'Entente Cordiale' in 1904?

Answer: prime minister of the united kingdom

Question: Who married the woman who was to become Queen Beatrix of the Netherlands, on 10 March 1966?

Answer:
beatrix