<prompt> CO2 increases ventilation by acting mainly on receptors ofApneustic centerPneumotaxic centerVental surface of medullaDRG  <response>: In the medulla, the ventral respiratory group VRG consists of four groups of neurons that make up the exhalation expiratory area of respiratory control. ... The VRG contains both inspiratory and expiratory neurons. In quiet, restful breathing, the ventral respiratory group of neurons are inactive Ref: guyton and hall textbook of medical physiology 12 edition page number: 370,371,372 