State one method by which carbon dioxide is added to the air.

Explanation

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks for one method by which carbon dioxide (CO2) is added to the air.

2. **Identifying Sources of CO2**: There are several natural and anthropogenic (human-made) processes that contribute to the increase of CO2 in the atmosphere.

3. **Combustion of Fossil Fuels**: One significant method is the combustion of fossil fuels. This includes burning coal, oil, and natural gas for energy. When these fuels are burned, they react with oxygen to produce carbon dioxide and other gases.

4. **Decomposition of Lime Water**: Another method is the decomposition of lime (calcium carbonate) during cement manufacturing. When limestone is heated, it breaks down into lime and carbon dioxide, releasing CO2 into the atmosphere.

5. **Conclusion**: Therefore, one method by which carbon dioxide is added to the air is the combustion of fossil fuels.

**Final Answer**: One method by which carbon dioxide is added to the air is the combustion of fossil fuels.

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