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: Pathology
[{'content': 'Mottled enamel is due to: \nSelect and explain. \nA. Vitamin A deficiency, B. Excess of fluoride, C. Vitamin D deficiency, D. Teratogens', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]