In the Pathway a + B $\to$ C + D, Enzyme X Facilitates the Reaction

In the pathway A + B $\to$ C + D, enzyme X facilitates the reaction. If compound D inhibits enzyme X, you would conclude that

A) enzyme X is an allosteric inhibitor of the above reaction.
B) compound D is an allosteric stimulator of the above reaction.
C) compound D is a competitive inhibitor of the above reaction.
D) enzyme X is subject to feedback stimulation.
E) compound D is a coenzyme in the above reaction.