Earthworms are commonly found in

Options

A. Deep water
B. Saline water
C. Upper layer of the soil
D. Air

Explanation

**Step-by-Step Solution:**

1. **Understanding Earthworms**: Earthworms are classified as terrestrial invertebrates, meaning they primarily live on land rather than in water or air.

2. **Analyzing the Options**: The options provided are:
- Deep water
- Saline water
- Upper layer of the soil
- Air

3. **Eliminating Water Options**: Since earthworms are terrestrial organisms, we can eliminate the options related to water (deep water and saline water).

4. **Considering the Remaining Options**: We are left with two options: "Upper layer of the soil" and "Air".

5. **Identifying Earthworm Habitat**: Earthworms thrive in moist environments, specifically in the upper layer of soil, which provides the necessary moisture for their survival.

6. **Respiration Mechanism**: Earthworms respire through their skin via diffusion, which requires a moist environment. They do not have specialized respiratory organs.

7. **Physical Characteristics**: Earthworms are long, narrow, and cylindrical with no appendages. They have a pointed anterior end and a rounded posterior end.

8. **Conclusion**: Given that earthworms require moist conditions for respiration and are found in the upper layer of soil, the correct answer is "Upper layer of the soil".

**Final Answer**: Earthworms are commonly found in the upper layer of the soil.

---