Question

A biologist wants to increase the rate of his chemical reaction but has a limited amount of enzyme. He continues to increases the substrate concentration instead. Eventually, the reaction rate levels off, and he can't get it to go any faster. What prevented the rate from increasing further?
A- The solution ran out of enzyme
B-The substrate concentration reached Vmax
C- The products of the reaction inhibited the enzyme
D- The solution ran out of reactants.

Thank you if you can help!!!!