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 was the computer's name in 2001: A Space Odyssey?

Answer: 2001: a space odyssey


Question: Which is the only Avril Lavigne song to have reached No.1 in the US Billboard Chart?

Answer: avril lavigne


Question: What was the title of the 2006 BBC TV series about a group of postmen in Manchester?

Answer:
bbc one