Pick out the pollutant.

Options

A. Carbon monoxide
B. Oxygen
C. Nitrogen
D. Hydrogen

Explanation

To identify the pollutant from the given options, let's analyze each option step by step:

1. **Understanding Pollution**: Pollution refers to the unwanted changes in the characteristics of air, water, and soil. The agents responsible for causing these changes are called pollutants.

2. **Identifying the Options**:
- **Carbon Monoxide**: This is a well-known air pollutant. It is produced from the incomplete combustion of fossil fuels, burning of wood, combustion of automobiles, and agricultural waste. Therefore, carbon monoxide is indeed a pollutant.
- **Oxygen**: This is not a pollutant. Oxygen is essential for respiration and is a vital component of the air we breathe.
- **Respiration**: This is a biological process and not a pollutant. It refers to the process by which living organisms take in oxygen and release carbon dioxide.
- **Hydrogen**: This is also not a pollutant. Hydrogen is a gas that can be found in the atmosphere but does not contribute to pollution.

3. **Conclusion**: Among the given options, carbon monoxide is the only pollutant. Therefore, the correct answer is carbon monoxide.

### Final Answer:
The pollutant is **Carbon Monoxide**.

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