Which is most likely a source of air pollution?

The correct answer is B. CFCs.

Chlorofluorocarbons (CFCs) are chemicals that can deplete the ozone layer and contribute to air pollution. They are often found in aerosol sprays, refrigeration, and air conditioning systems. While littering, oil spills, and runoff can harm the environment, they are typically associated more with land and water pollution rather than air pollution.