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

[Q]: Which film was based on the story The Sentinel by Arthur C Clarke?
[A]: arthur c. clarke

[Q]: What is the title of the four-episode special of 'Doctor Who', made for the Red Nose Day telethon in the UK, broadcast in March 1999?
[A]: doctor who

[Q]: Which actor was the first director of the National Theatre ?
[A]:
actor