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': 'In simplified oral hygiene index, how many surfaces of the teeth are examined? \nSelect and explain. \nA. 6, B. 12, C. 18, D. 24', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]