causative agents
cluster
collective
communication
congestion
contact
copy space
crowd
crowded
crowded train
doll
epidemic
flock
flu
full house
gets crowded
human
human model
hustle and bustle
image
infected persons
infection
many people
miniature
model
more than one
outbreaks
pass each other
passing
people
people come and go
prevention
virus
white back
white background