In exception to cell theory is :

Options

A. viruses
B. bacteria
C. cyanobacteria
D. eukaryotes

Explanation

### Step-by-Step Solution:

1. **Understanding Cell Theory**:
- Cell theory states that all living organisms are composed of cells, and the cell is the basic unit of life. It also states that all cells arise from pre-existing cells.

2. **Identifying Exceptions**:
- To answer the question, we need to identify organisms that do not fit into the standard definition of the cell theory.

3. **Considering Viruses**:
- Viruses are unique entities that do not conform to the characteristics of living organisms as defined by cell theory. They are composed of nucleic acids (DNA or RNA) surrounded by a protein coat but lack cellular structures.

4. **Characteristics of Viruses**:
- Viruses do not have protoplasts (the living part of a cell).
- They cannot grow or reproduce independently; they require a host cell's machinery to replicate.
- Viruses can crystallize, which is a characteristic of non-living entities.

5. **Conclusion**:
- Given these characteristics, viruses are classified as exceptions to the cell theory because they exhibit traits of both living and non-living entities but do not fit neatly into either category.

### Final Answer:
The exception to cell theory is **viruses**.

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