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

Example Input: The Brooklyn Bridge crosses which river?
Example Output: brooklyn bridge

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

Example Input: What is the name of frozen carbon dioxide?
Example Output:
carbon dioxide