A fire can be extinguished by removing __________.

Correct Answer: Option D — any of the above

The fire tetrahedron consists of fuel, heat, oxygen, and a chemical chain reaction. Extinguishment is achieved by removing any one of these elements: fuel (starvation), heat (cooling), or oxygen (smothering). Removing the chain reaction (inhibition) is also effective, particularly with dry chemical agents used in engine room firefighting.