Answer:
C) mixture.
Step-by-step explanation:
The air that is breathed is formed by a mixture of gases: nitrogen (78%), oxygen (20%), noble gases (1%), carbon dioxide (0.03% and water (0.97%). The noble gases are the following: argon, neon, helium and krypton.Of that gas mixture the most important of all is oxygen, which is necessary for the breathing process and which is used for many important functions in the body.