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

Example Input: Physics. What is the SI unit for amount of substance?
Example Output: amount of substance

Example Input: Released last month, People, Hell and Angels is a posthumous album made up of songs recorded by which artist in 1969 ?
Example Output: angel

Example Input: Which online bookstore was originally called Cadabra.com?
Example Output:
amazon.com