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': 'During activation of a scaling instrument, the facial\nsurface of the blade and the tooth surface should form an angle of \nSelect and explain. \nA. > 15 but < 45, B. > 30 but < 60, C. > 45 but < 90, D. 90 but < 180', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]