Which activity would best keep the world's oxygen supply from decreasing? a. planting trees in forests that have been harmed b. changing jungles into farmland c. cutting down forests to sell wood d. clearing trees from areas near rivers

The statement that would best keep the world's oxygen supply from decreasing: 
a.Planting trees in forests that have been harmed 
Trees decrease the urban heat island effect via evaporation cooling and lessening the amount of sunlight that reaches parking lots and buildings. 

a.Planting trees in forests that have been harmed 

Almost half of the world's oxygen was supplied by phytoplanktons thru the process of photosynthesis.

The other half is produced on land by trees, and other plants via sunlight (photosynthesis) also.  To stop the world’s oxygen supply from decreasing, we must plant trees that have been harmed. 

Reactants are mean lol

The one that would be the most effective means of controlling current water pollution of us surface water is : shutting down factories that discharge materials to the rivers.the largest sum of us pollution currently caused by factory-related substance