Answer:
The correct answer is A. the presence of a positively charged residue in the S1 binding pocket.
Explanation:
The S1 pocket is basically a deep hydrophobic pocket, which permit long uncharged amino acids like tryptophan and phenylalanine to fit inside chymotrypsin. B
Binding inside the S1 pocket, places the adjacent peptide bond at the active sites for cleavage.