You are presented with the question "a breathing mask keeps what from being inhaled and causing health problems?" and the following answer choices: 
- cigarettes
 - harmful particles
 - chemical changes
 - influenza
 - oxygen particles
 - hydrogen and oxygen
 - air particles
 - atmosphere particles

Now knowing that abreathing mask is used for keeping harmful particles from entering the respiratory system and when inhaled, the particles lodge in the respiratory system, causing or aggravating health problems, choose the best answer.


 

  harmful particles       