TASK DEFINITION: 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.
PROBLEM: Category: DONKEYS & ELEPHANTS 
Clue: Or would you rather be one of these? (a cross between a male donkey & a female horse)

SOLUTION: mule

PROBLEM: Category: SUN 
Clue: In the main reaction making the sun's energy, 2 of these nuclear particles fuse & one becomes a neutron

SOLUTION: protons

PROBLEM: Category: U.S. BIZ 
Clue: The fiscal year 2009 sales of this Bentonville, Arkansas companv were $401 billion

SOLUTION:
walmart