OPT:
1). body
2). eyes
3). air
4). skin
5). gullet
6). nose
7). ears
8). lungs
Q: Fact 1: Abreathing mask is used for keeping harmful particles from entering the respiratory system. Fact 2: Oxygen enters the respiratory system through the mouth and the nose. Given the two facts above, breathing masks are used to keep harmful particles from entering the mouth and the what?
A:
6).