Which Explains the Relationship Between the Gas Pressure Gradient of the Atmosphere

Which explains the relationship between the gas pressure gradient of the atmosphere and the alveolar air that allows inhalation?

A) When atmospheric pressure is less than the pressure within the lung, air flows down this gas pressure gradient. Then air moves from the atmosphere into the lungs.
B) When atmospheric pressure is greater than the pressure within the lungs, air flows down this gas pressure gradient. Then air moves from the atmosphere into the lungs.
C) When atmospheric pressure is greater than the pressure within the lung, air flows away from this gas pressure gradient. Then air moves from the lungs out into the atmosphere.
D) When atmospheric pressure is less than the pressure within the lung, air flows up this gas pressure gradient. Then air moves from the atmosphere into the lungs.