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': 'Coefficient of thermal expansion of amalgam is: \nSelect and explain. \nA. 7.2a(ppm k-1)., B. 10.0(ppm k-1)., C. 25.0(ppm k-1)., D. 48.5(ppm k-1).', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]