What is true of a substrate?

A. It is not consumed or change by a reaction

B. It provides a reaction with energy

C. It acts as a product in a chemical reaction

D. It acts as a reactant in a chemical reaction

Answer: option D. it acts as a reactant in a chemical reaction.

The substrate is the the chemical species in an organic reaction that reacts to form other product, so the substrate is a reactant. The enzymes can act over specific substrates to accelerate the reaction. While the enzymes are not consumed (they are catalysts) the substrates are consumed.