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': 'Example for symptom index \nSelect and explain. \nA. OHI Index, B. Plaque Index, C. Bleeding Index, D. DMFT', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]