Answer:
Option A (air)
Explanation:
Scientists believe that the weakening of Earth's ozone layer could be caused by **air pollution**.
Option A (air) is the correct choice in this context. Ozone depletion is primarily linked to pollutants released into the atmosphere, such as chlorofluorocarbons (CFCs), which break down ozone molecules in the stratosphere. Therefore, the correct answer is **A. air**.