Two Students Measured an Equilibrium Constant for the Same Chemical

Two students measured an equilibrium constant for the same chemical reaction. Ken obtained a value of 130 for the equilibrium constant, but Barbie obtained a value of 11.4. The instructor checked their results and said they were both correct. How can that be?

A) The values vary according to the way the measurement is made. Ken must have measured product concentrations, while Barbie measured reactant concentrations.
B) The values vary according to the starting conditions of the reaction prior to equilibrium. Ken must have started with all reactants, while Barbie must have started with all products.
C) The values vary according to the stoichiometric coefficients that are used. The balancing coefficients that Ken used must have been twice those that Barbie used.
D) The values vary according to direction of the reaction. Ken must have used the reverse reaction.
E) The instructor must have made a mistake as the equilibrium constant for a reaction must always be the same.