Respiration in mollusca takes place by

Options

A. Body surface
B. Gills or ctenidia
C. Pulmonary sac
D. All of these

Answer

### Step-by-Step Solution:

1. **Understanding Mollusca**: Mollusca is a diverse group of animals that have soft bodies and are often protected by a hard shell. They are primarily aquatic but can also be found in terrestrial environments.

2. **Respiration Methods**: Mollusca can respire through various structures:
- **Body Surface**: Some mollusks can exchange gases directly through their skin, especially those that live in moist environments.
- **Gills (or Ctenidia)**: Most aquatic mollusks have gills located in the mantle cavity, which are specialized for extracting oxygen from water.
- **Pulmonary Sac**: Terrestrial mollusks, like some land snails, have developed a pulmonary sac that functions similarly to lungs, allowing them to breathe air.

3. **Conclusion**: Since mollusks can respire through their body surface, gills, and pulmonary sacs, the correct answer to the question "Respiration in mollusca takes place by" is:
- **Option D: All of these**.