You are presented with the question "what does a breathing mask keep harmful particles from entering?" and the following answer choices: 
- skin
 - tissue
 - stomach
 - h2o
 - H20
 - air
 - lungs
 - gas masks

Now knowing that abreathing mask is used for keeping harmful particles from entering the respiratory system and pulmonologists treat lungs and respiratory systems, choose the best answer.


 

       lungs  