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

[EX Q]: Which major river has its source at the confluence of the rivers Brigach and Breg in the Black Forest?
[EX A]: breg

[EX Q]: Of all the actors who played Doctor Who in the TV series of the same name, who appeared in the most episodes?
[EX A]: doctor who

[EX Q]: Which 1979 features characters called Ripley, Dallas, Brett and Lambert?
[EX A]:
dallas