Which statement describes how enzymes and substrates are related?
a) the enzyme influences the speed of change from substrate to product.
b) enzymes are released as substrates in a chemical reaction.
c) an enzyme is a special kind of substrate in a chemical reaction.
d) substrates combine with enzymes to form reactants.

The answer is A) The enzyme influences the speed of change from substrate to product.

Enzymes are biological catalysts. That means they increase the speed of change from substrate to product. Enzymes remain unchanged during the reaction they catalyze. 

Through the process of elimination:
B) is eliminated because enzymes are not released as substrates. These two are different molecules in the reaction.
C) An enzyme is not special kind of substrate.
D) Substrates combine with enzymes not to form reactants, but to form products.