Some enzymes are produced as zymogens because
a) the reactions they catalyze are undesirable at the site of production
b) they must have both an active site and an allosteric site, and these can't be produced simultaneously
c) the actual enzyme molecules are so large that they must be produced in pieces and assembled as needed
d) the pH at the site of production is very different from the pH at the site where they are used
e) no correct response