Understanding Greenhouse Gases
Greenhouse gases (GHGs) are components of the Earth's atmosphere that trap heat, contributing to the greenhouse effect, which is essential for maintaining the planet's temperature. Among the various GHGs, the question highlights three significant ones: CO2, N2O, and CH4.

1. Carbon Dioxide (CO2)
- CO2 is the most prevalent greenhouse gas produced by human activities, primarily through fossil fuel combustion, deforestation, and various industrial processes.
- It has a long atmospheric lifetime, which means it can remain in the atmosphere for hundreds of years, significantly influencing global warming.

2. Nitrous Oxide (N2O)
- N2O is released during agricultural activities, particularly through the use of nitrogen-based fertilizers, as well as from fossil fuel combustion and certain industrial processes.
- This gas has a much higher global warming potential (GWP) than CO2, making it a potent contributor to climate change.

3. Methane (CH4)
- CH4 is released during the production and transportation of coal, oil, and natural gas. Additionally, it comes from livestock and other agricultural practices, as well as from the decay of organic waste in landfills.
- Methane has a GWP significantly greater than CO2 over a 20-year period, highlighting its impactful role in short-term climate change.

Conclusion
- Each of these gases contributes to the greenhouse effect in different ways, making option 'D'—“All of these”—the correct answer.
- Understanding these gases and their sources is crucial for developing strategies to mitigate climate change and reduce their impact on the environment.