Final answer:
The question addresses plumbing standards, indicating that a shutoff valve is required immediately ahead of each water-supplied appliance and slip joint to control the water supply for maintenance or emergencies.
Step-by-step explanation:
The question pertains to plumbing standards, specifically the requirements for valves in plumbing systems. According to standard plumbing codes, immediately ahead of each water-supplied appliance and each slip joint or appliance supply is required a shutoff valve. This valve allows for the control and isolation of the water supply to the appliance for maintenance or in case of a leak. The installation of a shutoff valve ensures that water can be quickly turned off in an emergency without affecting the water supply to the rest of the building.