Air pollution is a serious environmental problem. It is mainly caused by vehicle exhaust fumes, industrial factories, and the burning of fossil fuels. Air pollution can lead to various health problems, such as respiratory diseases, and also contributes to global warming. Planting more trees can help clean the air.
What is mentioned as a primary cause of air pollution in the text?
A) Planting trees.
B) Respiratory diseases.
C) Vehicle exhaust fumes.
D) Global warming.