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 currency is used on Christmas Island?

Answer: christmas island


Question: Who was Prime Minister of Australia at the outbreak of World War I?

Answer: australia


Question: From which film, for which Chaplin film wrote the music, did Petula Clark have a Number One with 'This Is My Song'?

Answer:
charlie chaplin