Main cause of eutrophication is:

Options

A. Fluctuation of temperature
B. Unsual growth of aquatic vegetation
C. Enrichment of nutrients
D. Abundance of microorganisms

Answer

### Step-by-Step Solution:

1. **Understanding Eutrophication**:
- Eutrophication is a process that leads to the aging of lakes and other water bodies. It is primarily caused by the increase of nutrients in the water, which can lead to excessive growth of algae.

2. **Identifying Causes of Eutrophication**:
- The question provides several options to choose from regarding the main cause of eutrophication:
- A) Fluctuation of temperature
- B) Unusual growth of aquatic vegetation
- C) Enrichment of nutrients
- D) Abundance of microorganisms

3. **Analyzing Each Option**:
- **Option A**: Fluctuation of temperature - While temperature can affect aquatic ecosystems, it is not a primary cause of eutrophication.
- **Option B**: Unusual growth of aquatic vegetation - This is a consequence of eutrophication rather than a cause.
- **Option C**: Enrichment of nutrients - This refers to the increase of nutrients (like nitrogen and phosphorus) in water bodies, which is the main cause of eutrophication.
- **Option D**: Abundance of microorganisms - This can occur as a result of eutrophication but is not the main cause.

4. **Conclusion**:
- After analyzing the options, the correct answer is **C) Enrichment of nutrients**. This nutrient enrichment leads to algal blooms, which are a characteristic feature of eutrophication.

### Final Answer:
The main cause of eutrophication is **C) Enrichment of nutrients**.

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