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: STATES' SOUTHWEST CORNERS 
Clue: This state's is just north of the Columbia River
washington

Category: DRAMA 
Clue: Sula & Helena are robotesses in this Karel Capek play
"r.u.r."

Category: MUSIC APPRECIATION 
Clue: Types of this vocal music include Ambrosian, Byzantine & Gregorian

chants