This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Medicine
[{'content': "What is true about acute rheumatic fever? \nSelect and explain. \nA. Mitral valve is invariably associated, B. Earliest symptom is migratory arthritis, C. Sydenham's chorea is always present., D. It follows streptococcal skin infection", 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]