Gas exchange involves the transport of two respiratory gases, oxygen and carbon dioxide. review how each gas is transported between the atmosphere and the cells of your body by completing this exercise.

During inhalation, the diaphragm and rib muscles contract, increasing the volume of the lungs. Air enters the nose or mouth and flowsdown the trachea, bronchi, and bronchioles, and into the alveoli.During exhalation, the diaphragm and rib muscles relax, decreasing the volume of the lungs. Air leaves the alveoli and flows up thebronchioles, bronchi, and trachea, and exits through the nose or mouth

Dis the answer and i know because i took the quiz

Its either a) or b),wind and water erosion gradually widen the canyon