An enthalpy level diagram for a reaction with an intermediate is shown. The diagram has reactants on the left, a high transition state, an intermediate at a lower (but still elevated) plateau, a second transition state, and products on the right. Arrow A is the small enthalpy difference between reactants and products. Arrow B is the activation energy from reactants to the first transition state. Arrow C is the difference between reactants and the intermediate. Arrow D is the difference between the intermediate and the products. Which arrow shows the enthalpy change for this reaction?