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': '"Brush heap" structure is found in: \nSelect and explain. \nA. Zinc oxide impression material, B. Agar, C. Condensation silicone, D. Polyether', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]