contamination caused by unwanted matter.
Mainly pollution.
Mainly exhaust from cars.
las Vegas
china
in some countries they can be by predators and mainly pollution
agriculture
There are many pollutions factors in the US but it is mainly from cars.
Pollution mainly.
The gas that causes the biggest amount of air pollution has to be carbon dioxide. Due mainly to emissions from vehicles.
Mainly pollution and the link below will give further information.
nature has ample for man's need but not for man's greed....
Its mainly because of pollution, deforestation & increasing population .