Which of the following statements is true about the rate of a chemical reaction? A. The rate of a chemical reaction is dependent only on the concentration of the reactants. B. The rate of a chemical reaction is dependent only on the temperature at which the reaction occurs. C. The rate of a chemical reaction is dependent on the concentration of the reactants, the temperature at which the reaction occurs, and the presence of a catalyst. D. The rate of a chemical reaction is not affected by the presence of impurities in the reactants.