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 popular Doctor Who villains, it was revealed in 2011, are to be given 'a rest' by scriptwriters?

Answer: doctor who


Question: Which English comedian has joined Amanda Holden as one of the judges on the current series of 'Britain's Got Talent'?

Answer: britain's got talent


Question: Among the countries in Africa, which one has the largest economy?

Answer:
africa