Excretory organs of flatworms are

Options

A. Malpighian tubules
B. Nephridia
C. Protonephridia
D. Nephron.

Answer

### Step-by-Step Solution:

1. **Identify the Phylum**: Flatworms belong to the phylum Platyhelminthes. The term "Platy" refers to flat, and "helminthes" means worms.

2. **Understand Excretory Organs**: Excretory organs are responsible for the removal of waste materials, particularly nitrogenous waste.

3. **Identify the Excretory Organ in Flatworms**: The primary excretory organ in flatworms is called **protonephridia**.

4. **Structure of Protonephridia**: Protonephridia consist of flame cells, which are specialized cells that help in the filtration and excretion process.

5. **Evaluate Other Options**:
- **Malpighian tubules** are found in arthropods and are not associated with flatworms.
- **Nephridia** are found in annelids and mollusks, not flatworms.
- **Nephrons** are the functional units of the kidney in humans and are also not related to flatworms.

6. **Conclusion**: The correct answer is that the excretory organs of flatworms are **protonephridia**.

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

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