Estuaries are

Options

A. Freshwater wetlands
B. Salt water wetlands
C. Least productive ecosystem
D. None of the above

Explanation

**Step-by-Step Solution:**

1. **Understanding Estuaries**: Estuaries are coastal areas where freshwater from rivers and streams meets and mixes with saltwater from the ocean. This mixing creates a unique brackish water environment.

**Hint**: Remember that estuaries are not purely freshwater or saltwater; they are a mix of both.

2. **Characteristics of Estuaries**: Estuaries are typically partially enclosed by land and have a free connection to the sea. This means that they are influenced by both riverine and marine processes.

**Hint**: Think about how the geography of an estuary allows for the mixing of different water types.

3. **Ecosystem Productivity**: Estuaries are known to be among the most productive ecosystems on Earth. They provide rich habitats for a variety of species and serve as nurseries for fish and other marine life.

**Hint**: Consider why the mixing of nutrients from rivers and the ocean contributes to high productivity.

4. **Identifying the Correct Answer**: Given the options provided in the question, the correct answer is that estuaries are classified as saltwater wetlands due to their brackish water composition.

**Hint**: Focus on the term "saltwater wetlands" and how it relates to the presence of both freshwater and saltwater in estuaries.

5. **Eliminating Incorrect Options**: The other options (freshwater wetlands, least productive ecosystem, none of the above) do not accurately describe estuaries. Freshwater wetlands lack the saltwater component, and estuaries are highly productive, not least productive.

**Hint**: Analyze each option critically to see if it aligns with the definition and characteristics of estuaries.

**Final Answer**: Estuaries are saltwater wetlands.