Fact 1: Abreathing mask is used for keeping harmful particles from entering the respiratory system.

Fact 2: Air pollution is caused by the build-up of harmful gases and particles in the air.

Given the two facts above, answer the question "What does a gas mask keep out?" with the following options: 
- disease
 - The atmosphere
 - heat energy
 - air pollution
 - energy barrier
 - Bodily water
 - Dehydration
 - bacteria


 

    air pollution     