Which of the following classes of amplifier would provide the highest efficiency in the output stage of a CW, RTTY or FM transmitter?

Class C amplifiers offer the highest efficiency but achieve this by heavily distorting the amplitude of the input signal. However, modes like CW, RTTY, and FM are constant-envelope modes, meaning they do not rely on amplitude variations to carry information. Because all the data is contained in the frequency, phase, or simple on/off keying of the signal, these modes are completely unaffected by the severe amplitude distortion created by a Class C amplifier. Therefore, a CW, RTTY, or FM transmitter can safely use a Class C amplifier in its final output stage to take full advantage of its high electrical efficiency, whereas AM or SSB transmitters would require linear amplifiers like Class A, AB, or B.