Lichen deserts indicate

Options

A. air pollution due to CO
B. air pollution due to `SO_(2)`
C. pollution due to smoke
D. noise pollution

Answer

### Step-by-Step Solution:

1. **Understanding Lichens**: Lichens are a symbiotic association between fungi and algae. They are sensitive to environmental changes and can indicate the health of an ecosystem.

2. **Role as Pollution Indicators**: Lichens are known to be good indicators of air quality. They are particularly sensitive to certain pollutants, especially sulfur dioxide (SO2).

3. **Impact of Pollution on Lichens**: In areas with high levels of sulfur dioxide, lichens tend to be absent. This is because sulfur dioxide is harmful to them, and they cannot survive in polluted environments.

4. **Identifying the Type of Pollution**: The question asks what lichen deserts indicate. Since lichens are absent in areas with high sulfur dioxide levels, lichen deserts indicate air pollution, specifically due to sulfur dioxide.

5. **Conclusion**: Therefore, lichen deserts indicate air pollution, particularly from sulfur dioxide emissions, which are commonly associated with industrial activities.

### Final Answer:
Lichen deserts indicate air pollution due to sulfur dioxide.