Animals Use O₂ and CO₂ (PH) Levels to Regulate Ventilation

Animals use O₂ and CO₂ (pH) levels to regulate ventilation. Which of the following is CORRECT?

A) Water breathers primarily regulate ventilation in response to changes in CO₂ because their internal levels of CO₂ are very similar to water.
B) Water breathers primarily regulate ventilation in response to changes in CO₂ because O₂ is readily available from water.
C) Air breathers primarily regulate ventilation in response to changes in CO₂ because their internal levels of CO₂ are higher than for air.
D) Water breathers primarily regulate ventilation in response to O₂ changes as the level of O₂ in water is low.
E) Air breathers primarily regulate ventilation in response to changes in O₂ because O₂ is readily available from air.