Amplitude is roughly equivalent to:

A) frequency.
B) pitch.
C) loudness.
D) timbre.

Amplitude

Stimulus intensity; in audition, roughly equivalent to loudness, graphed by the increasing height of a sound wave.

Loudness

Loudness is the subjective perception of the intensity of sound, often measured in decibels, influencing how sound is experienced.

Frequency

The number of occurrences of a repeating event per unit of time, often used in the context of waves or cycles.