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

Example Input: Which is the only Avril Lavigne song to have reached No.1 in the US Billboard Chart?
Example Output: avril lavigne

Example Input: Which Dickens novel is subtitled The Parish Boy's Progress?
Example Output: charles dickens

Example Input: Which film was the directorial debut of Clint Eastwood in 1971?
Example Output:
clint eastwood