Final answer:
C) Ventilation. The respiratory action initiated by a signal from the medulla oblongata is inspiration. This is part of the process of pulmonary ventilation.
Step-by-step explanation:
The respiratory action initiated by a signal from the medulla oblongata is inspiration. The medulla oblongata contains the ventral respiratory group (VRG), which stimulates the contraction of accessory muscles involved in respiration to induce forced inspiration. The VRG also stimulates the accessory muscles involved in forced expiration. These actions are part of the process of pulmonary ventilation, which is the movement of air into and out of the lungs.