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

Ex Input:
Mr Barkis, Edward Murdstone and Tommy Traddles are all characters in which Charles Dickens novel?

Ex Output:
charles dickens


Ex Input:
Which novel by A J Cronin is credited with laying down the foundation in Great Britain for the introduction of the National Health Service?

Ex Output:
a. j. cronin


Ex Input:
The unification of the crowns of Aragon and Castile laid the basis of which modern-day European country?

Ex Output:

aragon