Which of these statements about enzymes is true? a.) enzymes increase the rate of a reaction by decreasing the gibbs free energy change of the reaction. b.) enzymes decrease the rate of a reaction by increasing the gibbs free energy change of the reaction. c.) enzymes increase the rate of a reaction by decreasing the activation energy of the reaction. d.) enzymes increase the rate of a reaction by decreasing the activation energy of the reaction and the gibbs free energy change of the reaction. e.) enzymes do not change the rate of a reaction?