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

Ex Input:
In music, which band consists of Billy Gibbons, Dusty Hill and Frank Beard?

Ex Output:
frank beard

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

Ex Output:
amount of substance

Ex Input:
Who wrote the Elvis Presley hit 'Blue Suede Shoes'?

Ex Output:
blue suede shoes