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
True regarding secular trends - 
Select and explain. 
A. Changes in disease pattern in terms of months, B. Changes in disease pattern seasonally, C. Changes in disease pattern over a short period of timer, D. Changes in disease pattern over a long period of time
D: Changes in disease pattern over a long period of time
Answer: D: Changes in disease pattern over a long period of time 
Explanation: None