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': 'Mc Kay discovered Colorado stain in: \nSelect and explain. \nA. 1901, B. 1897, C. 1908, D. 1930', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]