What two valves does the GND VENT switch close?

The correct choice indicates that the GND VENT switch is responsible for closing the Ground Vent Valve and the Recirculation Valve. Understanding the function of these valves is crucial for proper aircraft operation and safety.

The Ground Vent Valve is designed to manage the air pressure and flow within the cabin, especially during ground operations, where airflow dynamics are different than during flight. Closing this valve ensures that there is no unintended airflow or contamination that could affect the cabin environment when the aircraft is stationary.

The Recirculation Valve works alongside the environment control system to maintain a comfortable cabin atmosphere by recirculating cabin air. When the GND VENT switch closes this valve, it helps prevent potentially unfiltered or undesirable air from re-entering the cabin, particularly when the aircraft is on the ground.

The other options involve valves that do not directly relate to the cabin air management system during ground operations, focusing instead on fuel management, pressure relief mechanisms, and engine-related functions, which are not the primary concerns when addressing cabin ventilation in this context. Thus, the selection of the Ground Vent Valve and Recirculation Valve accurately reflects the system's design and operational focus.