Final answer:
An increase in carbon dioxide levels in the blood triggers an animal to breathe more deeply to expel excess CO₂ and intake more oxygen(OPTION C).
Step-by-step explanation:
An increase in carbon dioxide (CO₂) in the blood stimulates an animal to take a breath(OPTION C).
This occurs because as the level of CO₂ rises in the blood, it diffuses into the brain where it lowers the pH by increasing the concentration of hydrogen ions. This signals the respiratory centers in the brain to increase the rate and depth of breathing to expel the excess CO₂, thus increasing oxygen intake during inhalation.