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

Ex Input:
'Dookie' and '21st. Century Breakdown' are albums by which American rock band?

Ex Output:
21st century breakdown

Ex Input:
Which biologist was known as Darwin's Bulldog?

Ex Output:
charles darwin

Ex Input:
Carrie Fisher is the daughter of which actress?

Ex Output:
carrie fisher