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: Grace Anna Goodhue was the wife of which US President?

Answer: grace coolidge


Question: Which Dickens novel is subtitled The Parish Boy's Progress?

Answer: charles dickens


Question: Which branch of astronomy studies radiation with wavelengths greater than approximately one millimetre?

Answer:
astronomy