Which of the following describes alternating current?

Alternating current (AC) is defined by the periodic reversal of direction in the flow of electric charge. It continuously shifts from a positive voltage or current to a negative voltage or current and back again, creating a wave-like pattern. Direct current (DC), on the other hand, only flows in one direction. Even if a DC current pulses or drops to zero, it remains DC as long as it does not cross into the negative direction. Therefore, true alternating current must cross the zero point and reverse its polarity, moving continuously between positive and negative directions.