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': 'Sex and age is presented by: \nSelect and explain. \nA. Pyramid, B. Bar diagram, C. Both, D. None of the above', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Bar diagram', 'role': 'assistant'}]