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': 'Confidence limit is calculated by using \nSelect and explain. \nA. Mean and standard error, B. Mean and standard deviation, C. Median and standard deviation, D. Median', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]