You are answering a USMLE-style medical question. Question: A 70-year-old man with hyperlipidemia and hypertension returns to his cardiologist for ongoing blood pressure management. He reports feeling fine with no trouble with his medications. He exercises regularly and sleeps well without snoring or daytime somnolence. His blood pressure measurements in the past have ranged from 160 - 170/80 - 100 mmHg. Today, his pressure is 150/100 mmHg with a pulse of 65/min while on hydrochlorothiazide and ramipril. Physical exam reveals a II/VI early systolic murmur with split S2 is appreciated at the right upper sternal border. There is unremarkable carotid, renal, or abdominal bruits. What is the most common cause of his hypertension? Options: A) Primary hyperaldosteronism B) Hypothyroidism C) Stiffening of the aorta D) Aortic stenosis Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.