Final answer:
The voice becomes higher in pitch as the tension of vocal folds in the larynx increases, due to the direct relationship between tension, vibration frequency, and perceived pitch(option c).
Step-by-step explanation:
As the tension of vocal folds in the larynx increase, the voice becomes c)higher in pitch.
This is because pitch is determined by the frequency of the sound waves produced by the vibration of the vocal folds. Higher tension leads to faster vibration and a higher frequency, which we perceive as a higher pitch. Conversely, lower tension causes slower vibration and a lower frequency, resulting in a lower pitch. It is important to note that pitch and loudness are separate aspects of sound: pitch is related to frequency, while loudness is related to the amplitude of the sound waves.