Which of the following best describes "airframes"?

The term "airframes" refers to the integral structure of an aircraft that provides the necessary support for its various components and systems. This includes the fuselage, wings, and tail, which together form the framework that holds the aircraft's shape, supports aerodynamic forces, and houses systems like landing gear and control surfaces. An airframe is crucial for maintaining the aircraft's integrity and durability during flight and ground operations.

The other options describe different elements related to an aircraft: the propulsion system pertains specifically to the engines and associated mechanisms that provide thrust; the aerodynamic shape relates to the design features that optimize airflow; and the electronic systems encompass navigation, communication, and flight control technologies. While all these components are essential for an aircraft's overall functionality, they do not fall under the definition of the airframe itself, which is primarily about structural support.