This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Infectious Disease Epidemiology, Subject name: Social & Preventive Medicine
Endemic disease is defined as - 
Select and explain. 
A. Disease occuring regularly in expected frequency, B. Disease occuring irregularly, C. Disease occuring in excess of expected freqency, D. Disease affecting a large population
A: Disease occuring regularly in expected frequency
Answer: A: Disease occuring regularly in expected frequency 
Explanation: Ans. is 'a' i.e., Disease occuring regularly in expected frequency Sporadic - Disease occuring irregularly from time to time.Endemic - Disease occuring regularly in expected frequency.Epidemic - Disease occuring in excess of expected frequency.Pandemic - Epidemic affecting a large proportion of population over a wide geographic area.