Answer:
D. Zymogen activation.
Step-by-step explanation:
A zymogen refers to the inactive form of a protein molecule which gets activated by the action of the other enzyme.
The chymotrypsinogen is one such example which is secreted by the pancreas but remains inactive until it is activated by the trypsin.
The chymotrypsinogen is cleaved into peptide which then cleaves the amino acids with the aromatic amino acids like tryptophan and tyrosine. Thus after the conversion of chymotrypsinogen to the chymotrypsin, the enzyme helps in the digestion of the proteins.
Thus, Option-D is correct.