This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Communicable diseases, Subject name: Social & Preventive Medicine
True about epidemology of influenza - 
Select and explain. 
A. Asymptomatic seen rarely, B. Incubation period 10-12 hrs, C. Pandemic rare, D. Extra human reserviour seen
D: Extra human reserviour seen
Answer: D: Extra human reserviour seen 
Explanation: Influenza is an acute respiratory tract infection characterised by sudden onset of chills,malaise,fever,muscular pain anx cough. Influenza A strains are pandemic.Incubation period 18 to 72 hours Major reservoirs exists in animals and birds Reference; Park&;s Textbook of preventive and social medicine, 24th edition.Pg no. 163,164