Which of the following is a domain ?

Options

A. Archaea
B. Bacteria
C. Eukarya
D. All of these

Answer

To solve the question "Which of the following is a domain?" we will follow these steps:

### Step-by-Step Solution:

1. **Understand the Concept of Domain**:
- The term "domain" refers to the highest taxonomic rank in the biological classification system. It categorizes life forms into three major groups based on fundamental differences in their cellular organization.

2. **Identify the Options**:
- The options given are:
1. Archaea
2. Bacteria
3. Eukarya
4. All of these

3. **Review the Three Domains of Life**:
- The three domains of life, as proposed by Carl Woese, are:
- **Archaea**: This domain includes prokaryotic organisms that are distinct from bacteria and often live in extreme environments.
- **Bacteria**: This domain consists of prokaryotic organisms that are more common and diverse.
- **Eukarya**: This domain includes all eukaryotic organisms, which have complex cells with a nucleus.

4. **Analyze Each Option**:
- **Option 1: Archaea** - This is a domain.
- **Option 2: Bacteria** - This is also a domain.
- **Option 3: Eukarya** - This is likewise a domain.
- **Option 4: All of these** - Since all the previous options are domains, this option is correct.

5. **Conclusion**:
- Since all the provided options (Archaea, Bacteria, and Eukarya) are recognized as domains in the three-domain system of classification, the correct answer is **Option 4: All of these**.

### Final Answer:
**All of these**