You are answering a USMLE-style medical question. Question: A 16-year-old boy is brought to the physician by his parents for the evaluation of fatigue for several weeks. The parents report that their son quit doing sports at school because of low energy. The patient's academic performance has declined recently. He spends most of his time in the basement playing video games and eating bowls of cereal. He has no history of serious illness. His mother has Hashimoto's thyroiditis and his father has major depressive disorder. The patient does not smoke or drink alcohol. His vital signs are within normal limits. Examination shows conjunctival pallor, inflammation and fissuring of the corners of the mouth, and concavity of the finger nails. The remainder of the examination shows no abnormalities. Laboratory studies show: Hemoglobin 11.5 g/dL Mean corpuscular volume 76 μm3 Platelet count 290,000/mm3 Red cell distribution width 18% (N = 13%–15%) Leukocyte count 7,000/mm3 Which of the following is the most appropriate initial step in treatment?" Options: A) Regular blood transfusions B) Methylphenidate C) Iron supplementation D) Allogenic stem cell transplantation Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.