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: Social & Preventive Medicine
[{'content': 'Crippling fluorosis occurs at what level ? \nSelect and explain. \nA. 0.5-0.8 mg/litre, B. 1.5 mg/litre, C. 3-6 mg/litre, D. > 10 mg/litre', 'role': 'user'}, {'content': "Answer: D \nExplanation: Ans. is 'd' i.e., 10 mg/liter Crippling fluorosis This occurs at fluoride level > 10 mg/litre (PPM). Patient is crippled and bed ridden.", 'role': 'assistant'}]