Answer:
The correct answer is option d. "an enzyme"
Explanation:
Enzymes are naturally occurring catalysts that speed up a chemical reaction by lowering the activation energy needed for the reaction to take place. Enzymes are complex proteins in nature and are reusable since they are not denatured or destroyed as a result of the reaction. Enzymes are among the most important proteins in nature, since they regulate metabolism as well as the reactions needed for DNA replication and protein translation.
