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': 'Small brown spots on teeth of a child, less than 4 years old are commonly due to: \nSelect and explain. \nA. ECC, B. Deep caries, C. Staining, D. Fluorosis', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]