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

Ex Input:
In which range of mountains are the two highest peaks Aconcagua and Ojos Del Salado?

Ex Output:
aconcagua


Ex Input:
What's the name of Doctor Who's home planet ?

Ex Output:
doctor who


Ex Input:
Catherine Barkley, Helen Ferguson and Rinaldi are all characters in which World War I novel by Ernest Hemingway?

Ex Output:

world war i