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