In humans, the concentration of carbon dioxide in the plasma:
A. causes increased production of hydrochloric acid.
B. regulates breathing rate by its effect on the medulla.
C. causes inflammation of the tissues of the bronchial tubes.
D. regulates gastric acid production by forming carbonic acid.
The medulla oblongata at the base of the brain increases breathing rate if the amount of carbon dioxide increases. It does not regulate breathing rate by checking oxygen content.