You are answering a USMLE-style medical question. Question: A 40-year-old woman comes to the physician because of a 6-month history of difficulty sleeping and fatigue. Menses occur at irregular 35- to 50-day intervals and last 3–7 days. Her last menstrual period was 5 weeks ago. She has had an unintentional 10-kg (22-lb) weight gain over this period. She also reports decreased sexual desire and increased hair growth on her face and arms. There is no personal or family history of serious illness. She appears lethargic. Her temperature is 37°C (98.6°F), pulse is 80/min, and blood pressure is 150/90 mm Hg. Physical examination shows central obesity, increased pigmented hair over the chin and upper lip, and purple stretch marks on the abdomen. She has a prominent hump of fat over the base of the dorsum of her neck and decreased proximal muscle tone and strength. Serum studies show: Na+ 154 mEq/L K+ 2.8 mEq/L Cl- 103 mEq/L HCO3- 30 mEq/L Creatinine 0.9 mg/dL Glucose 236 mg/dL ACTH 2 pg/mL (N = 7–50) Which of the following is the most appropriate treatment for this patient?" Options: A) Adrenalectomy B) Polychemotherapy and radiation therapy C) Transsphenoidal hypophysectomy D) Partial nephrectomy Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.