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

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

Ex Input:
Charlie Chaplin who died on Christmas Day in 1977, co founded which film studio along with Mary Pickford, Douglas Fairbanks?

Ex Output:
douglas fairbanks

Ex Input:
What is the third largest port of Belgium, accessed by a canal 200 metres (660 feet) wide and 32 kilometres (20 miles) long, which ends near the Dutch port of Terneuzen?

Ex Output:
belgium