Final answer:
The correct answer is the external auditory meatus, which is the opening to the outer ear and leads to the ear canal, ending at the tympanic membrane, unlike the oval window that lies between the middle and inner ear.
Step-by-step explanation:
The opening to the outer ear is known as the external auditory meatus. This structure serves as the entryway for sound waves into the ear canal, which leads back to the tympanic membrane or eardrum, a critical part of the auditory system responsible for capturing vibrations caused by sound waves.
The tympanic membrane is not the opening to the outer ear; it is at the end of the ear canal. Similarly, the oval window is incorrect because it is part of the boundary between the middle ear and the inner ear, where it receives vibrations from the ossicle known as the stapes. The central function of the oval window is to transmit these vibrations to the fluid-filled cochlea of the inner ear, ultimately leading to sound transduction. Therefore, when identifying the entrance to the outer ear structure, the external auditory meatus is the accurate choice.