Answer: A. air
Step-by-step explanation:
Air pollution, a very big problem is the world's largest cities today, is the release of harmful substances to humans into the air. It can be both in gaseous form and in solid form.
Gaseous form examples are Car and Factory Emissions such as Nitreous Oxides and Solid forms include dust and pollen.
As seen in this explanation, the emission of gases from factories and cars contributes to Air pollution.