Which utility system utilizes exhaust heat to operate a second turbine for electricity generation?

The option indicating a combined-cycle system is accurate because this type of utility system is specifically designed to enhance efficiency by utilizing both gas and steam turbines. In a combined-cycle system, the exhaust heat generated from the gas turbine is not wasted; instead, it is employed to heat water in a steam generator. This steam then drives a second turbine, contributing to further electricity generation.

The dual use of both turbines maximizes the energy produced from the same fuel source, leading to improved efficiency and lower emissions compared to traditional single-cycle systems. This setup reflects a modern approach to energy generation, where recovering and utilizing waste heat plays a critical role in enhancing overall performance and sustainability.

In contrast, the other options do not relate to this concept. For example, a conductor refers to materials that allow the flow of electricity, while compatible vegetation and constraint triangles pertain to considerations in utility planning and operations rather than energy generation approaches. Thus, they do not pertain to the utilization of exhaust heat in electricity generation processes.