Answer:
(c) Pressure
Step-by-step explanation:
Sound is a pressure wave, which means it consists of variations in air pressure that travel through the air as a wave. When we visualize the waveform of a sound, we are typically representing the variations in air pressure over time.
The vertical axis of the waveform represents the amplitude of the pressure variations. This means that as the amplitude of the waveform increases, the pressure variations increase, and vice versa. Since the pressure variations are what make up the sound wave, it is logical to take pressure as the vertical axis for visualizing the waveform.