Which of the following best describes a prime mover?

A prime mover refers to a device that converts energy from one form into mechanical energy, which can then be used to drive machinery or generate electricity. In the context of this question, the best description of a prime mover is a steam turbine.

A steam turbine operates by using high-pressure steam to rotate blades connected to a shaft. This rotation can either produce mechanical work directly or be harnessed to drive an electric generator. The steam turbine effectively translates thermal energy from steam into kinetic energy and is thus a key component of many power generation systems.

The other choices, while related to power generation technologies, do not accurately define a prime mover. A type of steam engine is a specific category of engine that operates on a different principle and typically converts steam energy into mechanical work through pistons rather than rotating machinery like a turbine. A type of generator describes the electrical device that converts mechanical energy into electrical energy, and a type of boiler generates steam but does not perform the function of converting energy into mechanical form. Therefore, the steam turbine stands out as the appropriate representation of a prime mover.