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

Ex Input:
Who achieved fame for his ,'Confessions Of An English Opium Eater'?

Ex Output:
confessions of an english opium-eater


Ex Input:
Alexander the Great died in which ancient city?

Ex Output:
alexander the great


Ex Input:
Which group of the 1970's featured Tony Iommi on guitar, Geezer Butler on bass and Bill Ward on drums?

Ex Output:

geezer butler