Which three elements must be present for combustion to occur?

The presence of air, fuel, and an ignition source (heat) is essential for combustion to occur. Combustion is a chemical reaction that typically involves the rapid combination of a fuel with oxygen, producing heat and light.

Fuel serves as the combustible material, while air, which contains oxygen, is required to sustain the combustion process. The ignition source provides the necessary heat to initiate the reaction, ensuring that the fuel and oxygen can combine effectively. When all three of these elements are present, combustion can begin and be maintained.

This understanding is foundational in various applications, especially in heating systems like gas furnaces, where precise control of combustion elements is vital for safe and efficient operation. The other options presented do not accurately encapsulate the necessary elements for combustion in this context, highlighting the fundamental nature of air, fuel, and an ignition source as integral components of the combustion process.