How do steam engines primarily operate?

Steam engines primarily operate by converting thermal energy into mechanical energy. They achieve this process through the combustion of fuel, which generates heat that turns water into steam. The steam expands and moves under pressure, driving a piston or turbine, which in turn converts that steam's kinetic energy into mechanical work. This is the core principle of how a steam engine functions, making it an example of a thermal energy conversion system.

In contrast, options such as using electrical energy or relying exclusively on hydraulic pressure do not accurately represent the primary operating principles of steam engines. While mechanical levers may be involved in the machinery of a steam engine, they are not the main mechanism by which steam engines operate. The essence of a steam engine's functionality lies in its ability to transform thermal energy derived from the heat of steam into usable mechanical energy.