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': 'Sprue pin is attached to posterior teeth in \nSelect and explain. \nA. Cusp tip, B. contact area, C. marginal ridge, D. proximal surface', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]