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

[Q]: Who succeeded Jon Pertwee as Doctor Who?
[A]: doctor who

[Q]: Which river begins in the Rocky Mountains in south-west Colorado, crosses New Mexico and forms the border between Mexico and the USA before reaching the Gulf of Mexico?
[A]: new mexico

[Q]: The city of Akron is in which US state?
[A]:
united states