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
[{'content': 'Corrosion of amalgam restoration: \nSelect and explain. \nA. Can extend upto a depth of 100 - 500 μm, B. Decreases if tin content of alloy increase, C. Is promoted by gama phase of alloy particles, D. Is resisted the most by copper-tin phase in high copper amalgams', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]