Which of the following sets contains unicellular organisms only?

Options

A. Paramecium, Allium, Saccharomyces
B. Euglena, Chlorella, Chlamydomonas
C. Euglena, Saccharomyces, Allium
D. Rhizopus, Spirogyra, Solanum

Explanation

To determine which set contains only unicellular organisms, we need to analyze the options provided and identify the organisms in each set.

### Step-by-Step Solution:

1. **Understand the Definition of Unicellular Organisms**:
- Unicellular organisms are those that consist of a single cell. Examples include bacteria, some fungi, and certain protists.

2. **Examine the Options**:
- We need to look at each option provided in the question and identify the organisms listed.

3. **Identify Unicellular Organisms in Each Set**:
- **Set 1**: Paramecium (unicellular), Alien (multicellular), Onion plant (multicellular)
- Contains multicellular organisms, so this set is not correct.
- **Set 2**: Saccharomyces (unicellular), Uglina (unicellular), Cholera (unicellular)
- All organisms in this set are unicellular, making this a potential correct answer.
- **Set 3**: Rhizopus (multicellular), Spirogyra (unicellular), Solanum (multicellular)
- Contains multicellular organisms, so this set is not correct.
- **Set 4**: (Assuming there is a fourth set based on the context)
- Without specific organisms listed, we cannot analyze this set.

4. **Conclusion**:
- Based on the analysis, **Set 2** contains only unicellular organisms: Saccharomyces, Uglina, and Cholera.

### Final Answer:
The set that contains unicellular organisms only is **Set 2**.