Certain forests in dry climates periodically catch fire, which enables some seeds to germinate. What kind of disturbance is this?

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.