A mastermind puzzle

You're playing mastermind, an algorithmic and logical game (if you don't know the rules, you can google them). You've posed the following guesses so far, and got the following results (x is RIGHT color, RIGHT location, o is RIGHT color, WRONG location):

OYPR -- xx
YBOW -- xo
BWYY -- o

What one guess can you make, that regardless of being correct, will give you a definitive answer as to what the code is?

>>12
Should have used JS!