The correct answer is D) Working fluids are taken in, transformed, and then discarded. An open cycle gas turbine engine is best described by this statement because in an open cycle, the working fluid (air) is drawn in, compressed, heated, and then exhausted to the atmosphere rather than being recycled or recuperated. This is in contrast to a closed cycle gas turbine, where the working fluid is contained within the system and reused. The open cycle design is simpler and more common in applications such as aircraft propulsion, where the exhaust is used to generate thrust. The other answer choices are incorrect because: A) Energy is neither created nor destroyed in any thermodynamic cycle, not just an open cycle; B) External energy addition is a characteristic of all gas turbine engines, not specifically open cycles; and C) Recuperation of working fluids is a feature of closed cycle gas turbines, not open cycle engines.