Final answer:
The oral vestibule is the space between the gums, lips, and cheeks, framed internally by the gums and teeth and externally by the cheeks and lips. The option (D) is correct.
Step-by-step explanation:
The space between the gums, lips, and cheeks is called the oral vestibule. It is the pocket-like part of the mouth that is framed on the inside by the gums and teeth, and on the outside by the cheeks and lips. The broader area known as the oral cavity runs from the gums and teeth to the fauces.
While the cheek muscles, including the buccinator muscles, and the orbicularis oris muscle in your lips help keep food inside the mouth during chewing and aid in speech. Therefore, option (D) is correct.