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

Ex Input:
Who played Captain Jean-Luc Picard in the television series 'Star-Trek: The Next Generation'?

Ex Output:
jean-luc picard


Ex Input:
Aragon and Castile joined to form which country?

Ex Output:
aragon


Ex Input:
Which great river flows though China, Laos, Cambodia and Vietnam to the South China Sea?

Ex Output:

china