An example of a filamentous green alga is :

Options

A. Chlamydomonas
B. Volvox
C. Spirogyra
D. Fucus

Explanation

To determine an example of a filamentous green alga from the given options, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Definition**:
- Filamentous green algae are characterized by their structure, which consists of long, thread-like filaments.

2. **Analyze the Options**:
- The options provided are:
- a) Chlamydomonas
- b) Volvox
- c) Spirogyra
- d) Fucus

3. **Evaluate Each Option**:
- **Chlamydomonas**: This is a genus of unicellular green algae that are flagellated. They are not filamentous, so this option is incorrect.
- **Volvox**: This is also a genus of green algae that forms spherical colonies. It is not filamentous, hence this option is also incorrect.
- **Spirogyra**: This is a filamentous green alga. It consists of long, unbranched filaments and is commonly found in freshwater environments. This option is correct.
- **Fucus**: This is a genus of brown algae, commonly known as rockweed. It is not filamentous and is found in marine environments, making this option incorrect.

4. **Conclusion**:
- The only option that fits the description of a filamentous green alga is **Spirogyra**.

### Final Answer:
The correct answer is **Spirogyra**.

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