Virus are living because:

Options

A. They multiply in host cells
B. Carry annerobic respiration
C. Carry metabolic activity
D. cause infection

Answer

To determine why viruses are considered living organisms, we can analyze the options provided in the question step by step.

### Step-by-Step Solution:

1. **Understanding Viruses**:
- Viruses are unique entities that exist at the edge of living and non-living. They lack cellular structures, nuclei, and organelles that are typically found in living organisms.

2. **Analyzing the Options**:
- **Option A: They multiply in host cells**:
- This is a key characteristic of living organisms. Viruses can only reproduce by infecting a host cell and hijacking the host's cellular machinery to replicate their genetic material and produce new virus particles.
- **Option B: Carry anaerobic respiration**:
- Viruses do not perform respiration, whether aerobic or anaerobic. They do not have metabolic processes like living cells.
- **Option C: Carry metabolic activity**:
- Viruses do not carry out metabolic activities independently. They rely on the host's cellular machinery for any form of metabolism.
- **Option D: Cause infection**:
- While viruses do cause infections, causing an infection alone does not qualify them as living organisms. This is more of a consequence of their ability to multiply in host cells.

3. **Conclusion**:
- The most accurate reason for considering viruses as living entities is their ability to multiply in host cells. Therefore, the correct answer is **Option A: They multiply in host cells**.

### Final Answer:
Viruses are considered living because they multiply in host cells.

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