A Series of Enzymes Catalyze the Reaction X → Y

Multiple Choice

A series of enzymes catalyze the reaction X → Y → Z → A. Product A binds to the enzyme that converts X to Y at a position remote from its active site. This binding decreases the activity of the enzyme.
-What is substance X?

A) a coenzyme
B) an allosteric inhibitor
C) a substrate
D) an intermediate
E) the product