What type of electrical system uses alternating current?

The correct choice identifies that an AC system utilizes alternating current, which is fundamental to its operations. Alternating current is characterized by the continuous change in direction of the electrical current, alternating between positive and negative values over time. This is in contrast to direct current (DC), where the current flows in a single direction.

In electrical systems, AC is popular because it can be transmitted over long distances with less energy loss compared to DC. Both single-phase and three-phase systems are configurations of AC systems. A single-phase system typically consists of a single alternating voltage that can power small electrical loads, while a three-phase system combines three alternating currents, providing a more efficient way to transmit electricity for larger loads or industrial applications.

By identifying the AC system as the correct answer, it highlights the broader classification of electrical systems that utilize alternating current, embracing both single-phase and three-phase configurations within the AC spectrum, ultimately serving a variety of applications in residential, commercial, and industrial contexts.