Choose the statement that best describes the rate of a reaction:

• A. The speed at which the concentration of the reactants increases or the concentration of the products decreases over time.
• B. The speed at which the concentration of the reactants decreases or the concentration of the products increases over time.
• C. The speed at which both concentrations of reactants and products increase over time.
• D. The speed at which both concentrations of reactants and products decrease over time.

Answer: (B)