Fact 1: Blood pH may become unbalanced if the rate of breathing is too fast or too slow.

Fact 2: Breathing is regulated to keep as normal as possible arterial blood pH and PO2.

Given the two facts above, answer the question "what is regulated by breathing?" with the following options: 
- thirst
 - air pressure
 - blood flow
 - body water
 - Energy
 - Chemical energy
 - Decibels
 - kinetic energy


 

   blood flow      