Carbon Dioxide Levels in the Blood and in Cerebrospinal Fluid

Carbon dioxide levels in the blood and in cerebrospinal fluid affect pH of these fluids. This enables the organism to sense a disturbance in gas levels as ________.

A) the brain directly measures and monitors oxygen levels and causes breathing changes accordingly
B) neurons in contact with cerebrospinal fluid monitor pH and use this measure to control breathing
C) the brain alters the pH of the cerebrospinal fluid to force the animal to retain more or less carbon dioxide
D) stretch receptors in the lungs cause the medulla oblongata to speed up or slow breathing
E) the medulla oblongata is able to control the concentration of bicarbonate ions in the blood