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

[Q]: What was the last silent film in which Chaplin's little tramp appeared?
[A]: chaplin


[Q]: Who wrote `20,000 Leagues Under The Sea`?
[A]: 20,000 leagues under the sea


[Q]: Who has taken over the TV role of Doctor Who, from actor David Tennant?
[A]:
doctor who