In Considering the Active Site of Serine-Proteases, a Fair Generalization

In considering the active site of serine-proteases, a fair generalization is that

A) nearly all the amino acid side-chains of the protein must directly participate in catalysis.
B) all the amino acid residues which are involved in the active site are adjacent because they are located on the same short stretch of the polypeptide backbone.
C) the conformation of the active site region does not exist at all until the substrate is bound.
D) the amino acid residues which form the active site are in close proximity because of the specific three-dimensional conformation the protein has adopted.
E) only one amino acid residue is involved in the active site.