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: Which river begins in the Rocky Mountains in south-west Colorado, crosses New Mexico and forms the border between Mexico and the USA before reaching the Gulf of Mexico?

Answer: new mexico


Question: Miss Rosa Dartle is a character in which Charles Dickens novel?

Answer: james steerforth


Question: In Jules Verne's book 20,000 Leagues Under the Sea, who captained the submarine the Nautilus?

Answer:
twenty thousand leagues under the sea