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

[EX 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?
[EX A]: doctor who

[EX Q]: Cinder Cone, composite, and shield are all types of what?
[EX A]: cinder cone

[EX Q]: What example of a clipper ship built in 1869 is preserved in a dry dock at Greenwich, London?
[EX A]:
clipper