Which statement is true about ac? a). the electrons move back and forth b). the +/- polarity is constant c). it is most common in portable devices d). it can produce only low voltages

In a wire carrying Alternating Current, the electrons move "back and forth", first toward one end of the wire, then toward the other end of the wire. (A)

The + / - polarity of AC is constantly reversing. (B)

AC is most commonly used to power devices that plug into a wall outlet, and very very very seldom to power portable devices. (C)

AC is used at voltages anywhere between several hundred-thousand volts for long-distance interstate power transmission, to 3 or 4 volts coming out of a "wall wart" AC adapter in the house. (D) .  Voltage of an AC is easily shifted with a transformer, whereas transformers can't be used for DC.