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 most retentive type of pin is \nSelect and explain. \nA. Cemented pin, B. Self threading pin, C. Friction locked pin, D. amalgam pins', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]