Excretory organs of flatworms/Taenia are

Options

A. flame cells
B. protonephridia
C. Malpighian tubules
D. green glands

Explanation

### Step-by-Step Solution:

1. **Identify the Organism**: The question refers to flatworms, specifically Taenia (a genus of parasitic flatworms).

2. **Understand the Excretory System**: Flatworms possess a unique excretory system known as protonephridia. This system is essential for their osmoregulation and excretion.

3. **Define Protonephridia**: Protonephridia are a network of tubules that end in specialized cells called flame cells. These structures are responsible for the excretion of waste products and the regulation of osmotic pressure within the organism.

4. **Function of Flame Cells**: Flame cells are the functional units of protonephridia. They help in filtering waste from the body fluids and play a crucial role in maintaining ionic balance and osmotic pressure.

5. **Eliminate Incorrect Options**:
- **Flame Cells**: While they are part of the protonephridia, they are not the complete excretory organ themselves.
- **Malpighian Tubules**: These are excretory structures found in insects, not flatworms.
- **Green Glands**: These are excretory organs found in some crustaceans, not in flatworms.

6. **Conclusion**: The primary excretory organs of flatworms, including Taenia, are the protonephridia, which consist of flame cells.

### Final Answer:
The excretory organs of flatworms (Taenia) are **protonephridia**.

---