air
air quality
asia
asian
backpack
bag
boy
carbon dioxide
child
city
classmate
concept
coronavirus
covid19
danger
disease
education
elementary
epidemic
filter
flu
gas
hazard
health
infection
mask
medical
n95
pandemic
pm2 5
pollution
portrait
protection
protective
pupil
quarantine
respiratory
safety
school
schoolboy
schoolchild
schoolgirl
sick
student
uniform
urban
virus
warning
wearing
young