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': 'Acute rheumatic fever occurs most commonly in \nSelect and explain. \nA. 5-14 yrs, B. 15-20 yrs, C. 21-25 yrs, D. 26-30 yrs', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]