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': "CPITN: \nSelect and explain. \nA. Was observed for the first time by ADA in 1992, B. Scored by a special periodontal probe of length 3 to 5 mm backward for easy visibility, C. Measure 6 representative teeth in young people, D. Score of '3' means the treatment involves oral hygiene instructions, scaling and curettage", 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]