When a boiler is fed from the home’s water supply, you need to both control the pressure entering the boiler and protect the drinking water supply from any backflow. A pressure reducing valve lowers the incoming water pressure to a safe, stable boiler feed pressure so the system isn’t over-pressurized as water heats and expands. A backflow preventer sits in the supply line to stop boiler water from flowing back into the potable water system, preventing contamination if pressures change or a cross-connection exists. Together, these two components keep the boiler operating safely and shield the plumbing from backflow risks. Other devices like expansion tanks, air vents, or sight gauges are important for system hydraulics and maintenance, but they don’t provide the same combination of pressure control and backflow protection.

The main idea this question tests is understanding different blueprint viewpoints and what each one shows. An aerial view is the view from directly above the structure, capturing the overall footprint, roof lines, and how the building sits on the site. It focuses on the external shape and relationship to the surroundings rather than interior details. A floor plan, by contrast, shows the interior layout—rooms, walls, doors, and windows as seen from above but at about floor level. A cross section is like slicing the building vertically to reveal internal features along a cut line. An isometric drawing presents a 3D perspective that shows multiple faces at once. Because the question asks which plan corresponds to the aerial view, the term that matches that top-down, site-wide perspective is the aerial view.

A float switch is the sensing device that starts and stops a sewage ejector or effluent pump. It’s a buoyant mechanism placed in the pump basin that rises with the wastewater level. When the liquid reaches a preset height, the float switch closes the electrical circuit and powers the pump on. As the pump reduces the level, the float falls, opening the circuit and turning the pump off at a lower threshold. This level-based control is essential for automatic, reliable operation in a wet well or sump. Other devices aren’t the primary initiators here. A thermostat watches temperature, not liquid level. A pressure gauge measures system pressure and doesn’t directly start the pump. A switch relay can control the power circuit, but it’s driven by the float switch (or a control panel) rather than serving as the sensing element that triggers starting the pump.

Fall protection on scaffolds is required once you’re at a height where a fall could cause serious injury, which in this context is six feet above the lower level. At or above this height, barriers or safety systems must be in place—such as guardrails (typically a 42-inch top rail with a mid-rail) or a personal fall arrest system—so workers don’t fall from the platform. The six-foot mark is chosen because it represents a practical threshold for preventing dangerous falls on typical scaffold work. Four feet is below that threshold, so fall protection is not mandatory by the standard in this context. Eight feet and ten feet are higher than the minimum required height, but the question uses six feet as the trigger point, signaling that protection is required starting at that height.