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': 'Concentration of fluoride in salt \nSelect and explain. \nA. 225ppm, B. 250ppm, C. 275ppm, D. 90ppm', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]