Introduction:
Sound is a form of energy that is produced by vibrations. When an object vibrates, it creates sound waves that travel through the air and reach our ears, allowing us to hear different sounds. In the case of human beings, the production of sound occurs due to the vibration of certain organs and structures in the body.

Vocal Cords:
The correct answer to the question is option 'D' - vocal cords. The vocal cords, also known as vocal folds, are located in the larynx or voice box, which is a part of the respiratory system. The larynx is situated in the throat, just above the trachea or windpipe.

How Sound is Produced:
When we speak or produce sound, the air from our lungs is pushed out through the trachea and into the larynx. The vocal cords, which are two folds of tissue, come together and vibrate as the air passes through them. These vibrations produce sound waves, which then travel through the pharynx, nose, and mouth, ultimately reaching the external environment.

Role of Vocal Cords:
The vocal cords play a crucial role in the production of sound. When we speak, the muscles in the larynx adjust the tension of the vocal cords, controlling their vibration rate. The tighter the vocal cords are, the higher the pitch of the sound produced. Conversely, when the vocal cords are looser, the pitch is lower.

Other Organs Involved:
While the vocal cords are primarily responsible for producing sound, other organs and structures also contribute to the formation of different sounds. These include:

1. Lips: The lips help in shaping the sounds produced by the vocal cords. By modifying the shape and position of the lips, different vowel and consonant sounds can be created.

2. Tongue: The tongue also plays a crucial role in the production of sound. It helps in articulating different sounds by touching various parts of the mouth, such as the teeth, palate, and alveolar ridge.

3. Teeth: Although the teeth themselves do not produce sound, they are involved in the production of certain sounds. For example, the /th/ sound in words like "think" and "this" requires the tongue to touch the upper front teeth.

Conclusion:
In summary, the correct answer to the question is option 'D' - vocal cords. While the vocal cords are primarily responsible for producing sound through their vibrations, other organs such as the lips, tongue, and teeth also play important roles in shaping and articulating different sounds. Together, these organs and structures allow human beings to produce a wide range of sounds and communicate through speech.