Final answer:
A gas valve controls the flow of gas to the burners of a furnace, allowing it to start or stop.
Step-by-step explanation:
A gas valve is an important component of a furnace that controls the flow of gas to the burners. It acts as a stopper or a gate, regulating the flow of gas into the burners of the furnace. When the valve opens, gas is allowed to flow into the burners and ignite the fuel, creating a flame for heating purposes. When the valve is closed, the flow of gas is shut off, stopping the burners from receiving fuel. Therefore, option D is the correct answer.
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