You are answering a USMLE-style medical question. Question: A 9-month-old boy is brought to his pediatrician by his mother for a routine health checkup. The boy was born at 39 weeks gestation via spontaneous vaginal delivery. He is up to date on all vaccines and is meeting all developmental milestones. He was breastfed for the first 3 months and then switched to cow’s milk and about two months ago she started giving him fruits and vegetables. Family history is noncontributory. Today, his heart rate is 120/min, respiratory rate is 40/min, blood pressure is 90/50 mm Hg, and temperature of 37.0°C (98.6°F). On examination, he has a heartbeat with a regular rate and rhythm and his lungs are clear to auscultation bilaterally. Generally, the boy looks pale. His weight and height fall within the expected range. A complete blood count (CBC) shows the following: Hemoglobin (Hb): 9.1 g/dL Mean corpuscular volume (MCV): 65 fL Total iron binding capacity (TIBC): 550 μg/dL Serum iron: 45 µg/dL Serum lead: < 5 µg/dL What is the best treatment for this patient? Options: A) Iron supplementation only B) Proper diet and iron supplementation C) Multivitamins D) Proper diet only Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.