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
A radiopaque area is observed under a 3-month old silver amalgam filling. The base used most probably was: 
Select and explain. 
A. Calcium hydroxide, B. ZOE, C. Formocresol, D. Zinc oxyphosphate
A: Calcium hydroxide
Answer: A: Calcium hydroxide 
Explanation: None