Abreathing mask is used for keeping harmful particles from entering the respiratory system, and air pollution is caused by the build-up of harmful gases and particles in the air. Given these facts, what does a gas mask keep out among the following options:
- disease
 - The atmosphere
 - heat energy
 - air pollution
 - energy barrier
 - Bodily water
 - Dehydration
 - bacteria


 

    air pollution     