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

Fact 2: When inhaled, the particles lodge in the respiratory system, causing or aggravating health problems.

Given the two facts above, answer the question "a breathing mask keeps what from being inhaled and causing health problems?" with the following options: 
- cigarettes
 - harmful particles
 - chemical changes
 - influenza
 - oxygen particles
 - hydrogen and oxygen
 - air particles
 - atmosphere particles


 

  harmful particles       