Final answer:
Positive-pressure ventilation involves a machine applying positive pressure to push air into the lungs, and exhalation occurs due to increased intrathoracic pressure.
Step-by-step explanation:
During positive-pressure ventilation, the mechanics of breathing are artificially replicated by a machine. Instead of the body creating a negative pressure inside the thoracic cavity to draw air into the lungs, as occurs during normal inhalation, a positive pressure is applied by the ventilation device to push air into the lungs. Therefore, the correct answer to which of the following occurs during positive-pressure ventilation is d) Exhalation due to increased intrathoracic pressure. This increased pressure forces air out of the lungs during the exhalation phase of the ventilation cycle.