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: "TWO" 
Clue: It features Jefferson on the front & the signers of the Declaration on the back
two-dollar bill

Category: "E" BAY 
Clue: Thinking green, biologist Ernst Haeckel coined this term for the way animals interact with the environment
ecology

Category: COUNTRY MUSIC 
Clue: In 2002 this movie soundtrack won ACM awards for Album of the Year & Vocal Event for "I Am a Man of Constant Sorrow"

o brother, where art thou?