Final answer:
An excess flow valve should be provided upstream of a quick-disconnect in a gas supply system to prevent gas leaks and potential hazards.
Step-by-step explanation:
When a quick-disconnect is used on a gas supply system, a device called an excess flow valve should be installed upstream of the disconnect. This safety device is specifically designed to stop the flow of gas in the event of a significant increase in flow rate, such as what might occur if the gas line is ruptured or disconnected. These valves are crucial for preventing gas leaks and the subsequent risks of fire or explosion. The correct answer to the question is: c) An excess flow valve upstream of the disconnect. Excess flow valves are designed to automatically close and restrict the flow of gas if there is a sudden increase in gas flow, such as when a line is disconnected or ruptured.