The answer to this question is given as (a).why isn't it (c)?Please explain

Q5. Marginal utility (MU) in terms of money is equal to :

       (a) $\frac{\mathrm{marginal} \mathrm{Utility} \mathrm{in} \mathrm{units}}{\mathrm{Maginal} \mathrm{Utility} \mathrm{of} \mathrm{one} \mathrm{rupee}}$                                       (b) $\frac{\mathrm{Maginal} \mathrm{Utility} \mathrm{of} \mathrm{one} \mathrm{rupee}}{\mathrm{marginal} \mathrm{Utility} \mathrm{in} \mathrm{units}}$

      (c) $\frac{\mathrm{marginal} \mathrm{Utility} \mathrm{in} \mathrm{units}}{\mathrm{price} \mathrm{of} \mathrm{the} \mathrm{commodity}}$                                       (d) None of these