A primary pollutant is

Options

A. CO
B. DDT
C. `CO_(2)`
D. All of these

Answer

**Step-by-Step Solution:**

1. **Definition of Primary Pollutants**:
- Primary pollutants are substances that are emitted directly from a source into the environment. They are not formed by the transformation of other substances in the environment.

2. **Examples of Primary Pollutants**:
- Common examples include:
- Carbon monoxide (CO)
- Carbon dioxide (CO2)
- Sulfur dioxide (SO2)
- Nitric oxide (NO)
- Pesticides like DDT

3. **Identification of Primary Pollutants**:
- When evaluating if a substance is a primary pollutant, check if it is released directly from a source without undergoing any transformation.
- For instance, CO is released from the combustion of fossil fuels, making it a primary pollutant.

4. **Conclusion**:
- Based on the definitions and examples, we can conclude that substances like CO, CO2, and DDT are all considered primary pollutants as they are emitted directly from their sources.