The sun is a vital part of the earth, so if it changes energy levels, it will clearly have an affect on the earth. If the energy increases, it'll most likely dry out the grass and melt the snow, etc. If it decreases, the snow could freeze and change the climate.
Deforestation is the permanently destruction of the forest. Trees and other plants in the forest are being destroyed due to some illegal actions done by human. This kind of issues leads to erosion and flooding because there's no longer trees that can absorb water to prevent erosion and flooding.
Answer:
A countercurrent system a more efficient system for gas exchange. Because water is viscous, this would require a lot of energy, so the counter-current system is a more efficient way of increasing the amount of oxygen diffusing into the blood. The unidirectional flow of water is another advantage.
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