Forests serve as _______ for the world.

Forests serve as cleaning agent for the world.

Forest is a large area covered with trees. Trees help in maintaining the level of carbon dioxide in nature. Just like lungs helps in excreting carbon dioxide from the body, trees help in removing carbon dioxide from the atmosphere by utilizing and storing it in the form of food (glucose). Some forest animals vultures, crows,
jackals and insects feed on the dead animals. The remains of these dead animals (carcass) or the dead plants are further degenerated by microorganisms present in the soil of the forest land.

Because of all these reasons, forest serve as the cleaning agents, hence, option C is correct.