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': 'The minimum amount of fluoride required in common salt for caries reduction is \nSelect and explain. \nA. 100 mg/kg, B. 90 mg/kg, C. 200 mg/kg, D. 350 mg/kg', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]