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': 'The changes occuring in the disease frequency over many years is called - \nSelect and explain. \nA. Cyclic trend, B. Seasonal trend, C. Secular trend, D. None of the above', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]