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

[EX Q]: Who played Lionel Hardcastle in the TV series 'As Time Goes By'?
[EX A]: as time goes by

[EX Q]: Betty Driver played which role in Coronation Street?
[EX A]: betty driver

[EX Q]: What city's Dharavi slum has a population of about 700,000 in less than one square mile?
[EX A]:
dharavi