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

Ex Input:
Which alliteratively-named politician served as Abraham Lincoln's Vice-President between 1861 and 1865?

Ex Output:
abraham lincoln

Ex Input:
Who was the first person to sign the American Declaration of Independence?

Ex Output:
united states declaration of independence

Ex Input:
The Catskill Mountains lie mainly in which state?

Ex Output:
catskill mountains