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': '0.05% of NaF has concentration of F \nSelect and explain. \nA. 9000 ppm, B. 1000 ppm, C. 225 ppm, D. 250 ppm', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]