How Are Serine Proteases Regulated to Cleave Some Peptide Bonds

How are serine proteases regulated to cleave some peptide bonds more frequently than others?

A) Substrate conformation changes to hide certain cleavage sites on binding to enzyme
B) Small molecules block some sites
C) The enzyme dimerizes around the substrate
D) There is a b-pleated sheet interaction between enzyme and substrate
E) Zymogen can be activated only at certain sites