Organisms like lichens are very sensitive to the levels of

Options

A. carbon dioxide
B. sulphur dioxide
C. carbon monoxide
D. methane.

Explanation

### Step-by-Step Solution:

1. **Understanding Lichens**:
- Lichens are a symbiotic association between two organisms: algae and fungi. This means they live together and benefit from each other.

2. **Sensitivity of Lichens**:
- Lichens are known to be sensitive to various environmental factors, particularly air quality. They can indicate the levels of certain pollutants in the atmosphere.

3. **Identifying the Pollutant**:
- Among the gases mentioned (carbon dioxide, sulfur dioxide, carbon monoxide, and methane), lichens are particularly sensitive to sulfur dioxide (SO₂).

4. **Reason for Sensitivity**:
- The sensitivity of lichens to sulfur dioxide is due to their efficient absorption system. When exposed to high levels of sulfur dioxide, lichens absorb it rapidly, leading to an accumulation of sulfur in their tissues.

5. **Impact of Pollution**:
- High levels of sulfur dioxide in the environment can inhibit the growth of lichens. This is why they are often referred to as indicators of pollution; their presence or absence can reflect the level of air quality in a given area.

6. **Conclusion**:
- Therefore, the correct answer to the question is that lichens are very sensitive to sulfur dioxide.

### Final Answer:
Lichens are very sensitive to the levels of **sulfur dioxide**.

---