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
Discolouration of silver alloy is due to: 
Select and explain. 
A. Tarnish, B. Tarnish and corrosion, C. Wet corrosion, D. Dry corrosion
B: Tarnish and corrosion
Answer: B: Tarnish and corrosion 
Explanation: None