The main causes for air pollution

Option a) is correct as it accounts to 70% of the air pollution coming from vehicles which are abundant.

Option b) is incorrect as it possesses little threat to the environment. And health of the people.

Option c) is incorrect it uses coal as its main ingredient which relatively lower than the availability of vehicles.

Option d) is incorrect as eutrophication is the ecosystem response to the addition of artificial or natural substances in the water bodies thereby hampering only the water bodies.