Answer: Option D) cofactor that is an activator of the enzyme.
Explanation:
A cofactor is a non-organic component (usually a metal) of an enzyme or protein, that enhances its function. Good examples of Cofactors include iron in hemoglobin, zinc in carboxypeptidase.
Zinc at the active site of the enzyme, carboxypeptidase helps it in cleaving off aromatic amino acids.