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 country are the Angel Falls, or Kerepakupai Ven?

Answer: angel falls


Question: Which English town shares its name with the state capital of Delaware?

Answer: delaware


Question: Which major river of the USA forms the border between the states of California and Arizona?

Answer:
arizona