which refers to the highness or lowness of a sound?\no pitch\no amplitude\no frequency\no softness

Brief Explanations:

Pitch is the perceptual property of sound that allows us to order sounds on a frequency - related scale from low to high. Amplitude relates to loudness, frequency is a physical property related to pitch but pitch is the perceptual aspect, and softness is related to loudness not the high - low quality of sound.

Answer:

A. pitch