Final answer:
The larynx, pharynx, and oral cavity together form a closed tube, which allows for the resonance of sound in speech production.
Step-by-step explanation:
The larynx, the pharynx, and the oral cavity together form a closed tube.
This closed tube allows for the resonance of sound in the production of speech. The vibrations from the voice box cause the air in this tube to vibrate, creating sound waves that can be shaped and articulated by movements of the tongue and shaping of the mouth.
This closed tube is responsible for the distinct characteristics of different voices and speech sounds.