<span>Alveoli are specifically designed to quickly facilitate the exchange of gas from the lungs to the blood. They are very small, but with a very high surface area allowing a greater amount of gases to be exchanged in a comparatively short period of time.</span>
The process by which molten material moves through the Earth's mantle is known as convection current. This is simply demonstrated within a liquid, in this case molten material, in which the hottest materials rise and the colder materials sink. Convection currents in the mantle are the forces that help move plate tectonics.
Answer:
sun and electric heater
Explanation:
sun is the biggest source of heat energy
electric heater is also an example of heat energy as it warms us
