Which of the following describes smog?

The correct choice describes smog as a combination of carbon monoxide and sulfur dioxide, which accurately reflects the chemical nature of smog. Smog is a type of air pollution that arises from the interaction of various pollutants in the atmosphere, particularly in urban environments.

Historically, the term originates from "smoke" and "fog," indicating that it is a physical manifestation of pollutants, including these specific gases along with particulate matter. Carbon monoxide can be produced from burning fossil fuels, while sulfur dioxide is mainly generated from industrial processes and the combustion of materials containing sulfur. Thus, the presence of these pollutants together can lead to the formation of smog conditions, which are characterized by reduced visibility and can have serious health impacts on populations.

The other options, while related to pollution and air quality, do not provide a complete or accurate description of smog. Smog specifically relates to the chemical composition and atmospheric conditions that create a particular type of air quality issue, distinguishing it from general industrial pollution or merely suspended dust particles.