In contrast, _________ power cannot be transformed.

The correct answer is direct current (DC) power because it flows in a single direction and maintains a constant polarity. Unlike alternating current (AC), which periodically reverses its direction and can easily be transformed to different voltage levels using transformers, DC power cannot undergo this transformation process.

Transformers rely on the changing magnetic fields created by alternating currents to induce voltage. Since direct current does not create these changing magnetic fields, transformers cannot be used to step up or step down its voltage. This characteristic makes DC power more limited in terms of voltage modifications compared to AC power.

Understanding DC's behavior is crucial, especially in applications such as batteries and electronic systems, where stable and predictable power supply characteristics are required.