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: \nSelect and explain. \nA. Trend over sho passage of time, B. Trend over long passage of time, C. Periodic changes, D. Sudden explosive changes', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Trend over long passage of time', 'role': 'assistant'}]