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

Fact 2: Pulmonologists treat lungs and respiratory systems.

Given the two facts above, answer the question "what does a breathing mask keep harmful particles from entering?" with the following options: 
- skin
 - tissue
 - stomach
 - h2o
 - H20
 - air
 - lungs
 - gas masks


 

       lungs  