**Core Concept**
The external auditory meatus, also known as the ear canal, is a narrow tube that connects the outer ear to the eardrum. Its length is an important anatomical measurement that helps in understanding ear function and potential issues.

**Why the Correct Answer is Right**
The external auditory meatus is approximately 2.5 cm (1 inch) in length in adults. This length allows for the proper transmission of sound waves from the outer ear to the eardrum. The ear canal is lined with ceruminous glands that produce cerumen, or earwax, which helps to protect the ear from dust, bacteria, and other foreign particles. The external auditory meatus also contains cartilaginous and bony structures that provide support and help to maintain its patency.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the external auditory meatus is not as short as 1 cm, which would not allow for proper sound wave transmission.
* **Option B:** This option is incorrect because the external auditory meatus is not as long as 5 cm, which would be an unusually long ear canal.

**Clinical Pearl / High-Yield Fact**
It's essential to note that the length of the external auditory meatus can vary slightly among individuals, but a length of approximately 2.5 cm is generally considered normal.

**Correct Answer: C. 2.5 cm**