Elevons blend pitch and roll control. On a delta wing, the outer trailing-edge surfaces act as one control surface that can move symmetrically to create pitch moments (like an elevator) or differentially to create roll moments (like an aileron). This lets a single surface provide both functions, which suits the delta wing’s geometry. Elevators alone control pitch, ailerons alone control roll, and ruddervators—combining rudder and elevator—appear on V-tailed aircraft, not on delta wings.

The key idea is how the accumulator stores energy to keep hydraulic pressure when the pump isn’t running. When the engine-driven pump is supplying pressure, the system is normal because the pump is active. Once the engine is shut down, the pump stops, and any remaining pressure should come from the accumulator, which is precharged with gas to exert pressure on the fluid. If there’s no pressure after shutdown, it means the accumulator cannot provide that reserve—usually because there is no air (gas) pressure in the accumulator. Without that precharge, the stored energy is gone and the system pressure collapses as soon as the pump stops. An incorrectly set pressure regulator would affect pressure while the pump is running, not explain a sudden loss after shutdown. Air in the hydraulic system would cause symptoms during operation as well, not specifically the immediate drop after shutdown. A leak would generally show a pressure drop during operation as well, not only after shutdown.

The air data computer takes the pitot and static pressures (and temperature) and converts them into the main air data that pilots rely on: indicated airspeed, Mach number, and altitude. Those data streams feed the instruments that display speed and altitude to the crew. So the air data computer provides input to the Mach meters, the airspeed indicator, and the altimeter. In many installations the cabin pressurization system also uses related data from the same source (cabin rate sensor) to monitor how quickly cabin pressure is changing, which is why that item can appear in the same set of inputs. Standby instruments typically have independent sources, and flight management computers or secondary radar are not direct cockpit display instruments fed by the air data computer. Therefore, the set that best reflects what the air data computer feeds is the Mach meters, the airspeed indicator, the altimeter (with the cabin rate sensor as a related use).

The key idea is that an in-flight entertainment system needs a source of actual content in addition to the user interface and the seat-side processing. The passenger control unit is how the passenger selects options, and the seat electronic box handles decoding and control at the seat. The third major piece is the media source—the device that actually plays the content, such as a tape or DVD player. This provides the video and audio that are then distributed to the displays and speakers. A video projector isn’t typically part of most IFE setups since content is shown on screens at the seat or in overhead displays, a zone multiplexer is a routing/delivery component rather than the content source, and an amplifier, while important, is usually part of the distribution or seat electronics rather than the standalone third major component. So the media source best fits as the missing third piece.