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 tarnished layer of silver amalgam consists of: 
Select and explain. 
A. Sulphides of silver, B. Oxides of tin, C. Chlorides of tin, D. All of the above
A: Sulphides of silver
Answer: A: Sulphides of silver 
Explanation: None