Given a factoid/trivia type question, generate the topic of the question. The topic is the entity the question talks about.

Example Input: Which four letter word beginning with 'F' is a white crumbly Greek cheese, made from sheep's or goats milk and cured in brine?
Example Output: sheep

Example Input: Ride of the Valkyries is the official quick march of which branch of the British Army?
Example Output: british army

Example Input: Which actor is the husband of Billie Piper?
Example Output:
billie piper