This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Epidemiology, Subject name: Social & Preventive Medicine
[{'content': 'Which of the following is true about secular trend- \nSelect and explain. \nA. Road side accident is a good example, B. Due to environmental factors, C. Is due to normally occuring variation in herd immunity, D. Consistent change in a paicular direction over a period of time', 'role': 'user'}, {'content': 'Answer: D \nExplanation: The term secular trend implies changes in the occurrence of disease (i.e. Progressive increase or decrease)over a long period generally several years or decades (refer page no:66 park 23 rd edition.', 'role': 'assistant'}]