Explanation: For 100% amplitude modulation (AM) using a plate-modulated Class C amplifier, the sinusoidal audio power supplied to the plate circuit must be equal to one-half of the DC input power to the modulated amplifier stage. This ensures that the peak audio voltage variation matches the DC plate voltage, causing the total instantaneous plate voltage to swing from zero to twice the DC supply, achieving full modulation. Given the DC plate input power is 200 W: Required Audio Power = 0.50 * DC Input Power Required Audio Power = 0.50 * 200 W = 100 W. The amplifier's efficiency (60%) is relevant for calculating the RF carrier output power (200 W * 0.60 = 120 W) but is not used to determine the audio power required for 100% plate modulation when the DC input power is known. Therefore, 100 W is the correct value.