You are answering a USMLE-style medical question. Question: A 10-year-old boy is brought to the physician because of a generalized, non-itchy rash for 2 days. He has also had a fever and sore throat for 4 days. He has not received any routine childhood vaccinations. Examination shows a flushed face except around his mouth. A diffuse, papular, erythematous rash that blanches with pressure is seen over the trunk. Pharyngeal erythema and a red beefy tongue are noted. His leukocyte count is 11,200/mm3 (75% segmented neutrophils, 22% lymphocytes). Without treatment, this patient's current condition puts him at greatest risk for which of the following complications? Options: A) Coronary artery aneurysms B) Encephalitis C) Mitral valve regurgitation D) Minimal change disease Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.