the loudness of a person's voice depends on the A. force with which air rushes across the vocal folds B. strength of the intrinsic laryngeal muscles C. length of the vocal folds D. thickness of vestibular folds

Answer: A. force with which air rushes across the vocal folds

Explanation:

The human voice is produced in the larynx, whose essential part is the glottis. This is how the air coming from the lungs is forced during expiration through the glottis, making its two pairs of vocal folds to vibrate.

It should be noted that this process can be consciously controlled by the person who speaks (or sings), since the variation in the intensity of the sound of the voice depends on the strength of the breath.