Rate of an Enzyme- Catalyzed Reaction as a Function of Varying

Rate of an enzyme- catalyzed reaction as a function of varying reactant concentration, with the concentration of enzyme constant.
In the graph provided, why does the reaction rate plateau at higher reactant concentrations?

A) The rate of the reverse reaction increases with reactant concentration.
B) The reaction nears equilibrium at high reactant concentrations.
C) Feedback inhibition by product occurs at high reactant concentrations.
D) The activation energy for the reaction increases with reactant concentration.
E) Most enzyme molecules are occupied by substrate at high reactant concentrations.