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 graph, C. Stem leaf plot, D. Box and whisker plot', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ref:Park's Textbook of Preventive and Social Medicine 25th Ed", 'role': 'assistant'}]