Hydrilla is

Options

A. Phytoplankton
B. Floating hydrophytes
C. Submerged hydrophyte
D. Amphibian

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks to identify what Hydrilla is from the given options.

2. **Identifying the Options**: The options provided are:
- A) Phytoplankton
- B) Floating hydrophytes
- C) Submerged hydrophytes
- D) Amphibians

3. **Defining Hydrophytes**: Hydrophytes are aquatic plants that thrive in water. The term "hydro" refers to water, and "phytes" refers to plants.

4. **Analyzing Hydrilla**: Hydrilla, also known as water thyme, is a type of aquatic plant. It is specifically known to be a submerged hydrophyte, meaning it grows entirely underwater.

5. **Evaluating the Options**:
- **Option A (Phytoplankton)**: These are microscopic organisms that float in water and are not the same as Hydrilla.
- **Option B (Floating hydrophytes)**: These plants float on the surface of the water, which does not describe Hydrilla.
- **Option C (Submerged hydrophytes)**: This accurately describes Hydrilla as it grows completely underwater.
- **Option D (Amphibians)**: These are animals that can live both in water and on land, which is not applicable to Hydrilla.

6. **Conclusion**: Based on the analysis, the correct answer is **Option C: Submerged hydrophytes**.