Which of the following is NOT one of the three points of control for natural gas appliances?

The three points of control for natural gas appliances are designed to ensure safety and manage gas flow effectively. The appliance cock is the shut-off valve located at the appliance itself, allowing for the isolation of the appliance for maintenance or repair. The meter cock is situated at the gas meter and controls the flow of gas to the entire building or residence. The curb valve is found outside the building, typically near the property line, providing another point at which the gas supply can be shut off, usually for emergency situations or maintenance outside the structure.

The ground valve, however, is not considered one of the primary points of control for natural gas appliances within the context typically discussed in safety procedures and operational guidelines. This type of valve might be used in some specialized systems or configurations but does not serve as a standard or essential control point in most household or standard commercial applications. Therefore, identifying the ground valve as the correct answer aligns with understanding the established and commonly referenced points of control for natural gas appliances.