The following are the structural carbohydrate molecules :

Options

A. starch and glycogen
B. starch and cellulose
C. glycogen and cellulose
D. cellulose and chitin

Explanation

**Step-by-Step Solution:**

1. **Understand the Types of Carbohydrates**: Carbohydrates can be classified into two main categories: storage carbohydrates and structural carbohydrates.

2. **Identify Storage Carbohydrates**:
- **Starch**: This is a storage carbohydrate found in plants, particularly in tubers like potatoes and grains like rice.
- **Glycogen**: This is a storage carbohydrate found in animals, primarily in the liver and muscles.

3. **Identify Structural Carbohydrates**:
- **Cellulose**: This is a structural carbohydrate that is a key component of plant cell walls, providing rigidity and strength.
- **Chitin**: This is another structural carbohydrate found in the cell walls of fungi and the exoskeletons of arthropods.

4. **Analyze the Given Options**:
- **Starch and Glycogen**: Both are storage carbohydrates. (Incorrect)
- **Starch and Cellulose**: Starch is a storage carbohydrate, while cellulose is structural. (Incorrect)
- **Glycogen and Cellulose**: Glycogen is a storage carbohydrate, and cellulose is structural. (Incorrect)
- **Cellulose and Chitin**: Both are structural carbohydrates. (Correct)

5. **Conclusion**: The correct answer is that the structural carbohydrate molecules are cellulose and chitin.

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