Concept:A device that provides continuous power even when the main supply is interrupted is needed.Explanation:An uninterruptible power supply (UPS) contains a battery that supplies power instantly if the main electricity fails, ensuring a constant flow of power to the computer.A voltage stabilizer only regulates voltage, but it does not keep power flowing during an outage.Step-up and step-down transformers only change voltage levels, not provide backup power.Answer:A. uninterruptible power supply.