You are answering a USMLE-style medical question. Question: A previously healthy 35-year-old woman comes to the emergency department because of sudden weakness of her right arm and leg that started 3 hours ago. She returned from a business trip from Europe 3 days ago. She has smoked a pack of cigarettes daily for 10 years. Her only medication is an oral contraceptive. Her temperature is 38.0°C (100.4°F), pulse is 115/min and regular, and blood pressure is 155/85 mm Hg. Examination shows decreased muscle strength on the entire right side. Deep tendon reflexes are 4+ on the right. Babinski sign is present on the right. The left lower leg is swollen, erythematous, and tender to palpation. Further evaluation is most likely to show which of the following? Options: A) Patent foramen ovale B) Mitral valve vegetation C) Atrial fibrillation D) Carotid artery dissection Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.