Air pollution is caused mainly by the burning of fossil fuel, which include coal and oil. When coal is burned it releases a large number of airborne pollutants and toxins in the environment. It includes sulfur dioxide, nitrogen oxides, mercury and lead, and various other metals.
Carbon dioxide is considered as a good indicator of how much fossil fuel is burnt and how much of pollutant is released into the atmosphere.
Twins form in one of two ways: Identical twins occur when a single fertilized egg splits into two. Fraternal twins occur when two, separate eggs are fertilized by two, separate sperm.
