The correct answer is A) An open cycle discards the working fluid and a closed cycle retains the working fluid. In an open cycle gas turbine engine, the working fluid (typically air) is drawn into the engine, compressed, heated, and then exhausted to the atmosphere. This means the working fluid is discarded after a single pass through the engine. In contrast, a closed cycle gas turbine engine recirculates and reuses the same working fluid in a closed loop, rather than discarding it. The working fluid is heated by an external source and then passed through the turbine to produce power, before being cooled and recycled back into the system. The other options are incorrect because they do not accurately describe the key difference between open and closed cycle gas turbine engines, which is the retention or discarding of the working fluid.