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: Dental
[{'content': 'A progressive increase or decrease of a disease over a long period of time, generally several years or decades is known as \nSelect and explain. \nA. Secular trends, B. Cyclic trends, C. Seasonal trends, D. Periodic fluctuations', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]