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 CPITN probe was designed for the detection of \nSelect and explain. \nA. Supragingival calculus, B. Debris, C. Subgigival calculus, D. Subgigival stains', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]