What is the target of arrow D as per the provided information?

The correct answer identifies the Auxiliary Power Unit (APU) as the target of arrow D. The APU is crucial in aviation as it provides electrical power and pneumatic pressure while the aircraft is on the ground and is key for starting the main engines. It is typically located in a compartment on the aircraft, often at the rear.

Understanding why the APU is the correct target involves recognizing its function relative to other components such as emergency exits, fuel tanks, and wing flaps. While emergency exits are critical for safety in evacuations, they do not share a direct relationship with the term associated with arrow D. Similarly, fuel tanks are pivotal for the aircraft's operation but are not relevant to an arrow indicating the focus of this particular question. Wing flaps play a significant role in aerodynamics, aiding in lift and drag during flight, yet they also do not correlate with the APU's purpose. Thus, the information provided points to the APU as the indicated target effectively.