What distinguishes direct current (DC) from alternating current (AC)?

Direct current (DC) is characterized by its flow of electric charge in a single direction, making choice C the correct response. This unidirectional flow means that in a DC circuit, the voltage remains constant over time, and the current does not alternate direction. This characteristic is critical for applications such as powering electronic devices and onboard systems in batteries, where a stable voltage is necessary.

Understanding the nature of AC is also essential, as it alternates direction periodically, meaning the voltage and current change over time. This alternating flow is typically used in household power supplies and industrial applications because it is more efficient for long-distance transmission.

The other choices relate to misconceptions about AC and DC characteristics. For instance, the incorrect assertion about DC flowing in both directions would misrepresent its fundamental nature, which is strictly one directional. Similarly, while AC is indeed generated in a way that allows for varied applications like household power, it is not correct to say it flows in only one direction, as its oscillation is what allows for higher efficiency in electricity distribution.