Attached and directly affected by some of the nine cartilages associated with the larynx are two bands of elastic ligaments which form what are known as and allow us to speak.
a. vocal folds (true vocal cords)
b. the epiglottis
c. vestibular folds
d. the glottis

The correct answer is option a. "vocal folds (true vocal cords)".

Explanation:

The vocal folds are composed of twin bands of elastic ligaments of mucous membrane stretched horizontally. The vocal folds are key in creating sounds and are the structures that allow us to speak. The size of  the vocal folds determines the pitch of the voice, and its movement is controlled by the vagus nerve, which allows it to be open when breathing and vibrating when singing.

Vocal folds

Explanation:

The vocal folds also known as true cords are folds of the tissues in the throat which aids in producing sound through vocalization.

The pitch of sound is affected by the size of vocal cords. The vocal cords closes when a person is speaking vocal cords are closed and when the person is not speaking.

This structure help in producing the sound by supporting the larynx and cartilage around it.

i think the answer is b.

1. efficient use of space

2. elimination of groundwater contamination

3. energy generation

4. lower carbon footprint