You are answering a USMLE-style medical question. Question: A 68-year-old male comes to the physician for evaluation of right flank pain. He has a history of diabetes and peripheral artery disease. His blood pressure is 160/90 mm Hg. Physical examination shows abdominal tenderness and right flank tenderness. An ultrasound shows dilation of the right ureter and renal pelvis. Which of the following is the most likely underlying cause of this patient's condition? Options: A) Renal artery stenosis B) Benign prostatic hyperplasia C) Common iliac artery aneurysm D) Urethral stricture Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.