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': 'The most important cause for marginal failure of amalgam restoration is: \nSelect and explain. \nA. Increased creep, B. Decreased strength, C. Tarnish and corrosion, D. Delayed setting of the material', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]