This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Biostatistics, Subject name: Social & Preventive Medicine
[{'content': 'One standard detion in normal standard curev includes value- \nSelect and explain. \nA. 50%, B. 68%, C. 95%, D. 100%', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ref:Parks 23rd edition pg 849. 1SD : confidence limit = 68% 2SD : confidence limit = 95% 3SD : confidence limit = 99.7%', 'role': 'assistant'}]