32. In Michaelis-Menten enzyme kinetics, the Km (Michaelis constant) represents: (A) The product concentration at which the reaction rate is half of Vmax. (B) The enzyme concentration at which the reaction rate is half of Vmax. (C) The enzyme-substrate complex concentration at which the reaction rate is half of Vmax. (D) The substrate concentration at which the reaction rate is half of Vmax. (E) The rate constant of the enzyme-substrate complex formation.