The mechanism of increased PaCO2 to stimulate respiratory center is mainly due to（）

A. CO2 directly stimulates the central chemoreceptor in the medulla oblongata

B. CO2 increases H+ concentration in cerebrospinal fluid, which stimulates the central chemoreceptor in the medulla oblongata

C. H+ stimulates chemoreceptor of the carotid body

D. CO2 stimulates chemoreceptor of the carotid body

E. CO2 stimulates chemoreceptor of the aortic body