You are answering a USMLE-style medical question. Question: A 10-year-old boy is brought to the emergency department because he has not been able to walk since waking up that morning. His mother said that when he tried to get out of bed that he was unable to stand without support. He also complained of prickling in his hands and feet. Three weeks ago, he had a fever, dry cough, and a sore throat. The fever and sore throat subsided a week after they began, but the cough is persisting. He has no history of serious illness and takes no medication. His vital signs are within normal limits. The lungs are clear to auscultation. There is severe weakness in both lower extremities and mild sensory loss of the hands and feet. Knee and ankle jerk reflexes are absent. The remainder of the examination shows no abnormalities. Laboratory studies show: Hemoglobin 12.0 g/dL Leukocyte count 6000/mm3 Segmented neutrophils 64% Eosinophils 2% Lymphocytes 26% Monocytes 7% Platelet count 160,000/mm3 Erythrocyte sedimentation rate 27 mm/h Serum Na+ 138 mEq/L Cl- 101 mEq/L K+ 4.9 mEq/L HCO3- 26 mEq/L Ca2+ 9.7 mg/dL Creatine kinase 93 U/L A lumbar puncture is performed; cerebrospinal fluid analysis shows a leukocyte count of 2/mm3, a glucose concentration of 60 mg/dL, and a protein concentration of 91 mg/dL. Which of the following is the most appropriate next step in treatment?" Options: A) Intravenous immunoglobulin (IVIG) B) Prednisone C) Botulism antitoxin D) Gabapentin Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.