Explanation:
The correct answer is option B, which states that the moist skin in earthworms helps in respiration. This is because the skin of earthworms is thin, moist, and permeable to gases. Let's explore this in more detail:

Respiration in Earthworms:
1. Earthworms are terrestrial organisms that do not have specialized respiratory organs such as lungs or gills.
2. Instead, they rely on their thin, moist skin for respiration.
3. The moist skin allows gases, particularly oxygen and carbon dioxide, to diffuse in and out of the body.
4. The moisture on the skin helps to keep it moist and allows gases to dissolve, facilitating their exchange.
5. The oxygen from the surrounding environment diffuses into the earthworm's body, while carbon dioxide, a waste product of cellular respiration, diffuses out.

Importance of Moist Skin:
1. Moisture on the skin is crucial for the efficiency of respiratory exchange.
2. If the skin dries out, the exchange of gases becomes difficult, and the earthworm may suffocate.
3. The moist skin also acts as a protective barrier, preventing the worm's body from drying out and protecting it from external pathogens.
4. It also helps in maintaining the proper osmotic balance of the earthworm's body.

Other Functions of Earthworm's Skin:
1. Locomotion: While the moist skin primarily aids in respiration, it also plays a role in locomotion. The secretion of mucus from the skin helps the earthworm move smoothly through the soil.
2. Protection: The skin acts as a protective layer against physical damage and pathogens. It helps in preventing the entry of harmful substances and microorganisms into the body.

In conclusion, the moist skin of earthworms is essential for respiration as it allows for the exchange of gases with the environment. It also serves as a protective barrier and aids in locomotion. Therefore, the correct answer is option B - respiration.

They use moist skin for respiration so that there is no deposition of mucus on their skin...