Which one of the following statements about viruses is correct

Options

A. Nucleic acid of viruses is known as capsidd
B. Viruses possess heir own metabolic system
C. All viruses contain both RNA and DNA
D. Viruses are obligate parasites

Explanation

To determine which statement about viruses is correct, let's analyze the provided statements step by step:

1. **Understanding Viruses**:
- Viruses are small infectious agents that can only replicate inside the living cells of an organism. They are not classified as living organisms because they do not possess the cellular machinery necessary for metabolism and reproduction.

2. **Evaluating the Statements**:
- **Statement 1**: "Nucleic acid of viruses is known as capsid."
- This statement is incorrect. The nucleic acid (either DNA or RNA) is not called a capsid. The capsid is actually the protein coat that surrounds and protects the viral nucleic acid.

- **Statement 2**: "Viruses possess their own metabolic system."
- This statement is also incorrect. Viruses do not have their own metabolic system; they rely on the host cell's machinery to carry out metabolic processes.

- **Statement 3**: "All viruses contain both DNA and RNA."
- This statement is incorrect as well. Viruses can have either DNA or RNA, but not both simultaneously. DNA viruses are called DNA viruses, and RNA viruses are called RNA viruses.

- **Statement 4**: "Viruses are obligate parasites."
- This statement is correct. Viruses are indeed obligate parasites, meaning they cannot reproduce or survive without a host cell. They are strictly dependent on a host for their life cycle.

3. **Conclusion**:
- Among the statements provided, the only correct statement is that "viruses are obligate parasites."

### Final Answer:
The correct statement about viruses is: **"Viruses are obligate parasites."**

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