You are answering a USMLE-style medical question. Question: A 9-year-old boy is brought to a physician by his mother for evaluation of generalized weakness, increased urination, and increased thirst. The mother mentions that her boy is always tired, and seems to be getting worse. He prefers watching television rather than going out and playing with other kids. Furthermore, he has had frequent episodes of constipation since birth. Except for frequent cravings for salty foods, the boy eats a regular diet. The patient was delivered healthy and is fully immunized. The medical history is unremarkable, and he takes no medications. He has no siblings. His father is a banker and his mother is a librarian. The pulse is 90/min, the blood pressure is 110/75 mm Hg, and the respiratory rate is 15/min. He is in the bottom 10th percentile for height and weight according to his age. The remainder of the physical examination is unremarkable. He recently had a urinalysis that showed elevated urinary calcium excretion. Additional lab testing results are as follows: Serum electrolytes Sodium 135 mEq/L Potassium 3.2 mEq/L Chloride 95 mEq/L Plasma renin activity 10 ng/mL/hr (normal, 0.5–3.3 ng/mL/hr) Plasma aldosterone concentration 20 ng/dL (normal, 2–9 ng/dL) What is the most likely diagnosis? Options: A) Renal artery stenosis B) Bartter's syndrome C) Pheochromocytoma D) Gitelman's syndrome Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.