In a very broad sense, what is the difference between alternating current (AC) and direct current (DC)?

• A. DC: current runs in one direction; AC alternates back & forth
• B. AC: current runs in one direction; DC alternates back & forth
• C. DC and AC both alternate back and forth
• D. DC: current runs in one direction; AC remains stationary

Answer: (A)

At a broad level, the difference is about the direction of current flow over time. Direct current moves in one fixed direction—from the source through the circuit to the load. Alternating current reverses direction periodically, so the electrons continually change course as the voltage polarity swings. This simple distinction is exactly what the statement expresses: direct current is unidirectional, while alternating current reverses. The other descriptions mix up the behavior: AC does not stay in one direction, and DC does not alternate back and forth.