This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Enzymes, Subject name: Biochemistry
Serine proteases 
Select and explain. 
A. Hydrolyze peptide bonds involving carboxyl groups of serine residues, B. Are characterized by having several active sites per molecule, each containing a serine residue, C. Are inactivated by reaching with one molecule of di-isopropyl-fluorophosphate per molecule of protein, D. Are exopeptidases
B: Are characterized by having several active sites per molecule, each containing a serine residue
Answer: B: Are characterized by having several active sites per molecule, each containing a serine residue 
Explanation: It is otherwise called alpha-anti-proteinase or protease inhibitor. It inhibits all serine proteases (proteolytic enzymes having a serine at their active center), such as plasmin, thrombin, trypsin, chymotrypsin, elastase, and cathepsin. Serine protease inhibitors are abbreted as Serpins. They are enzymes with a serine residue at the active site and most of the proteolytic enzymes belong to this group, e.g. trypsin, chymotrypsin, clotting factors Serine proteases examples-Trypsin, Chymotrypsin,Clotting factorsRef: DM Vasudevan, Page no: 44