instruction:
Given a factoid/trivia type question, generate the topic of the question. The topic is the entity the question talks about.
question:
Which English king was married to Eleanor of Castile?
answer:
eleanor of castile


question:
Who played the character Gene Hunt in the UK TV series 'Life on Mars' and 'Ashes to Ashes'?
answer:
life on mars


question:
Who wrote the opera Dido and Aeneas ?
answer:

dido and aeneas