You are answering a USMLE-style medical question. Question: A 62-year-old man comes to the emergency department because of right-sided back pain, nausea, and dark urine. He reports alternating episodes of decreased urine output followed by a temporary increase in urine output for the past 2 days. In the past year, he has had two urinary tract infections. He has Crohn disease and underwent a small bowel resection 5 years ago. He currently takes mesalamine and a multivitamin. His father had recurrent kidney stones. His vital signs are within normal limits. Examination shows right costovertebral angle tenderness. Urinalysis shows 70 RBC/hpf and envelope-shaped crystals. A CT scan of the abdomen shows a 6-mm stone in the proximal right ureter and two 4-mm stones in the left kidney. Which of the following factors has most likely contributed most to this patient’s current condition? Options: A) Parathyroid gland adenoma B) Excess vitamin D C) Malabsorption of fatty acids D) High urine pH Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.