Answer:
The top of the mountain
Explanation:
The top of the mountain is where the air is under the least pressure and, a lesser amount of oxygen is present, along with that, because in the picture, the top of the mountain would have the least amount of air pressure, said air (specifically oxygen) will have more difficulty making it through your lung's selectively permeable membranes, and making it's way around your body in your red blood cells.
