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': 'Secular trend is demonstrated by: \nSelect and explain. \nA. Line diagram, B. Bar graph, C. Pie cha, D. Stem leaf plot', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Line diagram', 'role': 'assistant'}]