Explanation: TTL (Transistor-Transistor Logic) devices operate using specific voltage thresholds to distinguish between logic high (binary 1) and logic low (binary 0). For a TTL device powered by a 5.0-volt supply, the standard specification for a valid logic high input (Vih) is any voltage from 2.0 volts up to the supply voltage, or slightly above, provided it remains within the device's absolute maximum input ratings (which can sometimes be up to 5.5V or 7V for short durations depending on the family). Therefore, option A, **2.0 to 5.5 volts**, correctly identifies this range. Any voltage at or above 2.0V will be interpreted as a logic high. Voltages below 2.0V but above 0.8V are considered an undefined or indeterminate region. Voltages at or below 0.8V are recognized as a logic low. Options B and C present ranges that are too low to reliably be interpreted as a logic high. Option D includes voltages far beyond the safe operating limits for a 5V TTL device, which would damage it.