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

Example Input: Grace Anna Goodhue was the wife of which US President?
Example Output: grace coolidge

Example Input: What's the name of Doctor Who's home planet ?
Example Output: doctor who

Example Input: Fictional character Detective Inspector John Rebus was created by which author?
Example Output:
detective inspector john rebus