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

Fact 2: Unlike larger particles, the smaller particles are able to enter the respiratory system.

Given the two facts above, answer the question "A breathing mask can prevent what kind of particle from entering the lung?" with the following options: 
- light
 - harmful
 - rabies
 - A virus
 - x-ray
 - deadly
 - ion
 - small


 

        small 