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': 'True about certain lethal dose (CLD): \nSelect and explain. \nA. 2 times of safely tolerated dose, B. 4 times of safely tolerated dose, C. 5 times of safely tolerated dose, D. 6 times of safely tolerated dose', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Fluoride toxicity:\n\nSafety recommended dose —\xa0Above 3 yrs old child is 1mg/day and\xa0adult 1.7 - 3.3 = 2.2 approx.\nSTD (safety tolerated dose) — 8 to 16 mgF/kg wt.\nCLD (certain lethal dose) — 32 to 64 mgF/kg wt (4 times of STD) = 56 g.\nProbable\xa0lethal dose = 5 mg/kg wt.\n\nEssentials of preventive and community dentistry\xa0\nSoben Peter\xa0\n5th edition', 'role': 'assistant'}]