You will be given a trivia clue, and the category it belongs to. You should answer with the best answer that belongs in the category and is described by the clue. For simplicity, answers should be in all lower cased letters.

Category: REMEMBRANCE OF THINGS "CAST" 
Clue: Hey, baby, you a Gemini?  These twin brothers of Helen of Troy are, literally
castor & pollux

Category: WORLD CITIES 
Clue: Intercontinental flights to Scotland land at Prestwick Airport just outside this city
glasgow

Category: BALLET 
Clue: As you might expect, "Doo Dah Day" is danced to the music of this composer

stephen foster