Final answer:
The theory that made it possible to build jet engines is the development of reliable and powerful engines, which included the advancement of new construction materials and electronic instrumentation and actuators.
Step-by-step explanation:
The theory that made it possible to build jet engines is the development of reliable and powerful engines. Initially, these engines were gasoline-powered piston engines, but in the 1940s, jet engines were developed and have since been improved to create today's highly efficient turbofan engines. Jet engines work by compressing air, burning fuel in the combustion chamber, and then accelerating the exhaust gases out the back of the engine, creating thrust.
In addition to the development of powerful engines, the advancement of new construction materials and electronic instrumentation and actuators have also played a significant role in building jet engines. The development of lightweight and strong metal alloys, as well as new composite materials, has allowed airplanes to become larger, carry larger payloads, and use fuel more efficiently. Electronic instrumentation and actuators enable airplanes to navigate in almost any weather conditions and include features like autopilots that control the plane and automatically navigate to a given destination.