Heat from burning fuel warms the walls of the firebox section of the furnace in

a. an evaporation system.
b. a compressor compartment.
c. a hot-air heating system.
d. a hot-water heating system.

C. a hot-air heating system.

Explanation:

The warm( or hot) air heating system uses a vent to pull in heat from the outside air and heats it over a gas flame. This warm air circulates via ducts, vents or grills which are located throughout the home. This heating systems are often managed by a thermostat.

So

Heat from burning fuel warms the walls of the firebox section of the furnace in

a hot-air heating system.

Option C is correct

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