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
The highest mercury concentration in amalgam filling is found 
Select and explain. 
A. At the margin of the restoration, B. In the centre of the restoration, C. In the deepest part of the restoration, D. None of the above
A: At the margin of the restoration
Answer: A: At the margin of the restoration 
Explanation: None