The correct answer is D. 1, 2, 3 and 4.
The steel industry is a major source of air pollution, releasing a variety of pollutants, including oxides of sulfur, oxides of nitrogen, carbon monoxide, and carbon dioxide. These pollutants can cause a variety of health problems, including respiratory problems, heart disease, and cancer.
Oxides of sulfur are released when sulfur-containing fuels, such as coal and oil, are burned. These pollutants can cause acid rain, which can damage forests, lakes, and other ecosystems.
Oxides of nitrogen are also released when sulfur-containing fuels are burned. These pollutants can contribute to smog and ground-level ozone, which can cause respiratory problems.
Carbon monoxide is a colorless, odorless gas that is released when fuels are burned incompletely. This pollutant can cause asphyxiation, especially in enclosed spaces.
Carbon dioxide is a greenhouse gas that contributes to climate change.
The steel industry is working to reduce its emissions of air pollutants. However, these emissions continue to be a major source of air pollution.