You are presented with the question "What does breathing help balance acidity levels?" and the following answer choices: 
- blood
 - muscles
 - water
 - air
 - CO 2
 - oxygen
 - Gases
 - protein

Now knowing that blood pH may become unbalanced if the rate of breathing is too fast or too slow and breathing is regulated to keep as normal as possible arterial blood pH and PO2, choose the best answer.


 

 blood        