Cyclic trend is shown by-

Ans. is 'd' i.e., All of the above Cyclic trend* Some diseases occur in cyclic spread over a short period of time which may be week, days, months or years.* This is due to naturally occuring variation in herd immunity.* A build up of susceptible is again required in the herd before there can be another attack.* It may be due to antigenic variations as occur in influenza.* Examples - Epidemic of# Measles - every 2-3 years# Rubella - every 6-9 years# Pandemic of influenza - every 10-15 years.