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': 'Which of the following is the main reason for resistance of enamel surface to demineralization? \nSelect and explain. \nA. Increased Phosphate content of surface layer, B. Decreased Magnesium content of surface layer, C. Increased Fluoride content of surface layer, D. Decreased Carbonate content of surface layer', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]