Which is most likely a source of air pollution?

The correct answer is B. CFCs.

Chlorofluorocarbons (CFCs) are chemical compounds that can deplete the ozone layer and contribute to air pollution when released into the atmosphere. They are often found in aerosol sprays and refrigerants. Littering, oil spills, and runoff primarily affect land and water quality rather than the air directly. If you have more questions or want further explanations, feel free to ask!