Explanation: A Class C amplifier operates with a bias beyond cutoff, meaning it only conducts for a portion of the input RF cycle. For proper operation and maximum efficiency, it requires strong radio-frequency (RF) excitation to drive the active device (tube or transistor) into full conduction during its conduction angle. If the RF excitation is insufficient, the amplifier cannot be driven hard enough. It will not achieve the necessary peak current and voltage swings, resulting in less actual output power than the amplifier is designed to deliver for a given average supply voltage. This consistent reduction in the average output power from its intended level is known as a **negative carrier shift**. The unmodulated carrier power is depressed. A positive carrier shift (B) would mean the average output power is higher than expected, which is the opposite of what insufficient excitation causes. Therefore, options C and D are incorrect.