An aircraft's integral fuel tank is?

An integral fuel tank is indeed a part of the aircraft's structure. Unlike traditional fuel tanks that are separate components that can be removed, integral fuel tanks are designed to utilize the aircraft's structure as the tank itself. This approach maximizes space within the aircraft and reduces weight by eliminating the need for a separate tank assembly. Integral tanks are typically designed into various parts of the aircraft, such as the wings or fuselage, which means they are not only structural elements but also serve the crucial function of fuel storage. This integration plays a significant role in achieving aerodynamics and fuel efficiency.

In contrast to the other options, integral fuel tanks are not usually flexible in terms of removal for maintenance, nor are they designed specifically with self-sealing capabilities like some separate tanks. The location of integral fuel tanks can vary but is most often found in the wings rather than primarily in the bottom of the fuselage.