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

Ex Input:
Angel Clare is a character in which novel by Thomas Hardy?

Ex Output:
angel clare

Ex Input:
Physics. What is the SI unit for amount of substance?

Ex Output:
amount of substance

Ex Input:
What did Bardeen, Shockley and Brattain invent in 1947, and for which they were awarded the Nobel Prize for Physics in 1956?

Ex Output:
walter houser brattain