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

Ex Input:
What is the SI unit of capacitance?

Ex Output:
capacitance

Ex Input:
Which two brothers had hits with Cathy's Clown and Wake Up Little Susie?

Ex Output:
cathy's clown

Ex Input:
Appassionata is a name given to Piano Concerto number 23 by which composer?

Ex Output:
piano sonata no. 23