You are answering a USMLE-style medical question. Question: A previously healthy 3-year-old boy is brought to the physician by his parents because of fever and a rash for 6 days. His temperature is 38.9°C (102°F). Examination shows right-sided anterior cervical lymphadenopathy, bilateral conjunctival injection, erythema of the tongue and lips, and a maculopapular rash involving the hands, feet, perineum, and trunk. Which of the following is the most common complication of this patient's condition? Options: A) Coronary artery aneurysm B) Rapidly progressive glomerulonephritis C) Hearing loss D) Retinopathy Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.