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': 'Standard error of mean is called as - \nSelect and explain. \nA. Standard detion, B. Mode, C. Median, D. Variable', 'role': 'user'}, {'content': 'Answer: A \nExplanation: .', 'role': 'assistant'}]