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': "Which of following is a composite index? \nSelect and explain. \nA. DMFT, B. OHI, C. Russel's index, D. OHI-S", 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]