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

Example Input: Kronos (or Cronus) was the Greek equivalent of which Roman god?
Example Output: cronus

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

Example Input: Who discovered the chemical elements Potassium, Sodium and Calcium?
Example Output:
potassium