During quiet breathing, which of the following pressure gradients is positive?

You're on a roll — The correct answer is B. Alveolar pressure during expiration. Here's why: Atmospheric pressure is the baseline, considered zero for reference. Inspiration (breathing in): To draw air into the lungs, the alveolar pressure must become negative (lower than atmospheric pressure). The intrapleural pressure also becomes more negative* during inspiration. Expiration (breathing out): To push air out of the lungs, the alveolar pressure must become positive (higher than atmospheric pressure). The intrapleural pressure remains negative* throughout the breathing cycle in a healthy individual, though it becomes less negative during expiration. Therefore, only alveolar pressure during expiration is positive compared to atmospheric pressure. What's next?