Answer:
Potential at the top. Kinetic when going down the hill.
Explanation:
Its basically mechanical energy! While at the top you have the potential to go down and race down using kinetic energy.
Plant trees because they absorbe co2
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.
I think that it is atmosphere but not 100% sure you might want to double check
