Succinic acid dehydrogenase is the enzyme that catalyzes the oxidation of succinic acid during cell respiration. If malonic acid is added to the system, the rate of reaction is reduced. An increase in the substrate concentration, succinic acid, increases the rate of reaction again. Using this information what might be deduced about the action of malonic acid?

A. It is an enzyme inhibitor.
B. It has a similar molecular configuration to that of succinic acid.
C. It decreases the pH of the system.
D. It acts as a coenzyme.