Two Students Measure the Equilibrium Constant for the Same Chemical

Two students measure the equilibrium constant for the same chemical reaction.One student finds K_c to be 130; the other calculates K_c to be 11.4.The instructor checks their results and says they are both correct.Which statement below is a plausible explanation?

A) The values vary according to the way the measurement is made.One student must have measured product concentrations whereas the second must have measured reactant concentrations.
B) The values vary according to the starting conditions of the reaction prior to equilibrium.One student must have started with all reactants whereas the second must have started with all products.
C) The values vary according to the stoichiometric coefficients that are used.The balancing coefficients that the first student used must have been twice those that the second used.
D) The values vary according to direction of the reaction.One student 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.