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': 'The ideal tooth - blade working angulation of a Blade of Gracey curette is angled from lower shank approximately at \nSelect and explain. \nA. 10 - 20 degree, B. 40 - 50 degree, C. 60 - 70 degree, D. 80 - 90 degree', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]