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

Which US state was the title of a no. 1 hit for the Bee Gees in 1967?
bee gees

Christian Grey is a character in what recent book trilogy?
christian grey

What mountain system in the USA stretches over 1500 miles south to Alabama, through which pass the Hudson and Mohawk Valleys?

alabama