You are answering a USMLE-style medical question. Question: A 76-year-old woman comes to the physician for a routine examination. She has a history of hypertension well controlled with diet and exercise. She has no history of smoking or illicit drug use. She walks one mile daily. Her pulse is 68/min, respirations are 16/min, and blood pressure is 119/76 mm Hg. Physical examination shows no abnormalities. When compared to a healthy 20-year-old woman, which of the following changes in respiratory function is most likely present in this patient? Options: A) Increased lung compliance B) Decreased residual volume C) Increased chest wall compliance D) Decreased A-a gradient Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.