Lichen indicate

Options

A. air pollution due to its sensitivity to CO.
B. air pollution due to its sensitivity 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. This means they consist of two different organisms that live together and benefit from each other.
- The fungal component provides structure and protection, while the algal partner, which is photosynthetic, produces food through photosynthesis.

2. **Role of Lichens in the Environment**:
- Lichens are sensitive to air quality, particularly to pollutants. They are often used as bioindicators to assess the level of air pollution in an area.
- They absorb various pollutants from the air, including sulfur dioxide and carbon monoxide.

3. **Sensitivity to Pollutants**:
- Lichens are particularly sensitive to sulfur dioxide. High levels of this gas can inhibit their growth and even lead to their disappearance in heavily polluted areas.
- The presence or absence of lichens can indicate the level of air pollution, especially regarding sulfur dioxide.

4. **Conclusion**:
- Given that lichens are sensitive to sulfur dioxide, their absence in an area can indicate high levels of air pollution due to this gas.
- Therefore, the correct statement regarding lichens is that they indicate air pollution due to their sensitivity to sulfur dioxide.

### Final Answer:
Lichens indicate air pollution due to their sensitivity to sulfur dioxide.

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