Combustion is the burning of a substance. It could be complete or could be incomplete. It changes the form of carbon and so it plays it's role in cycle
Lack of vitamin D has been linked to increased risk for autoimmune diseases.
Hope that helped you.
Frogs do have lungs but they are small and rarely used, frogs mostly take in moisture through the skin in process called cutaneous gas exchange.
Answer:
The return of blood to the heart is assisted by the action of the skeletal- muscle pump. As muscles move, they squeeze the veins running through them. Veins contain a series of one-way valves, and they are squeezed, blood is pushed through the valves, which then close to prevent backflow.
