You are answering a USMLE-style medical question. Question: A medical student is preparing a patient for an appendectomy. He is asked by the surgeon to disinfect the patient’s skin with a chlorhexidine-isopropyl alcohol solution before the procedure. Recent studies have shown that this solution substantially reduces the risk of surgical site infections compared with a povidone-iodine preparation without alcohol in clean-contaminated surgery. Which of the following mechanisms best describes the mechanism of action of chlorhexidine? Options: A) Bactericidal at low concentrations B) Cell wall damage by free radical release C) Attack of free-sulfur amino acids, nucleotides, and fatty acids within the bacteria D) Its activity depends on pH and is greatly reduced in the presence of organic matter Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.