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
"Brush heap" structure is found in: 
Select and explain. 
A. Zinc oxide impression material, B. Agar, C. Condensation silicone, D. Polyether
B: Agar
Answer: B: Agar 
Explanation: None