instruction:
Given a factoid/trivia type question, generate the topic of the question. The topic is the entity the question talks about.
question:
Who choreographed the ballets Swan Lake and Don Quixote, among others?
answer:
don quixote


question:
Which jockey won the 1981 UK Grand National on Aldaniti?
answer:
aldaniti


question:
The southern border of which country is with the continental USA?
answer:

united states