Consider an engine that undergoes a cyclical process, always returning to its initial state at the end of each cycle. According to the second law's second expression, what outcome is impossible for such an engine?

1. The second expression of the second law concerns cyclical engines, ones that return to their starting state at the end of every cycle. 2. It states that it is impossible for such an engine to convert heat transfer from a reservoir completely into work. 3. This means some heat transfer to a cold reservoir is unavoidable, which is the opposite of option B's claim that no such transfer can occur. 4. The law does not forbid engines from producing work at all, nor does it limit how many cycles an engine can run; it only forbids perfect conversion of heat into work, ruling out options A and C. _Source: OpenStax College Physics (CC BY 4.0), Ch 15 "Thermodynamics", section 15.3 Introduction to the Second Law of Thermodynamics: Heat Engines and Their Efficiency_