A) In amplitude modulation, the amplitude of the high-frequency carrier wave is made to vary in proportional to the amplitude of the audio signal.
B) In amplitude modulation, the frequency of the high-frequency carrier wave is made to vary in proportion to the amplitude of the audio signal.
C) In frequency modulation, the amplitude of the high-frequency carrier wave is made to vary in proportion to the amplitude of the audio signal.
D) In frequency modulation, the amplitude of the high-frequency carrier wave is made to vary in proportion to the frequency of the audio signal.
