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': 'True statement about Rheumatic fever in childrena) Polyarthritisb) Caused by α hemolytic streptococcic) Most common valve involvement is Mitrald) Erythema marginatum is common in face \nSelect and explain. \nA. bc, B. cd, C. ac, D. ab', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]