You are answering a USMLE-style medical question. Question: A 22-year-old man with sickle cell disease is brought to the emergency room for acute onset facial asymmetry and severe pain. He was in school when his teacher noted a drooping of his left face. His temperature is 99.9°F (37.7°C), blood pressure is 122/89 mmHg, pulse is 110/min, respirations are 19/min, and oxygen saturation is 98% on room air. Physical exam is notable for facial asymmetry and 4/5 strength in the patient's upper and lower extremity. A CT scan of the head does not demonstrate an intracranial bleed. Which of the following is the most appropriate treatment for this patient? Options: A) Alteplase B) Exchange transfusion C) Heparin D) Warfarin Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.