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': 'Stainless steel crown was introduced by \nSelect and explain. \nA. Humphrey, B. Stewart, C. Mac Donald, D. Pinhalm', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]