Answer:
The effiency decreases at higher altitudes
Explanation:
The higher up a person is on a mountain, the thinner the air is due to the lack of plants that can grow. An example of this is Mount Everest. At a certian point on the mountain, called the "Death Zone", the air is too thin to supply enough oxygen to the human body to survive. That's why they bring oxygen tanks with them on their adventures.
