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: Dental
[{'content': 'First clinical sign of localized juvenile periodontitis is \nSelect and explain. \nA. Tooth mobility, B. Gingival bleeding, C. Pathologic migration, D. Vertical bone loss along incisors and molars', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]