**Core Concept**
The "O" sign in a pure tone audiogram is indicative of a specific type of hearing loss, where the bone conduction threshold is greater than the air conduction threshold at a particular frequency. This is often seen in patients with otosclerosis, a condition characterized by abnormal bone growth in the middle ear.

**Why the Correct Answer is Right**
The "O" sign occurs due to the abnormal bone growth in otosclerosis, which causes the stapes bone to be fixed in place, leading to a conductive hearing loss. The bone conduction threshold is elevated because the abnormal bone growth prevents the normal transmission of sound through the middle ear. The air conduction threshold is normal because the problem lies in the middle ear, not the outer ear or the inner ear.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the "O" sign is not typically associated with sensorineural hearing loss, where the problem lies in the inner ear or the auditory nerve.
**Option B:** This option is incorrect because the "O" sign is not typically associated with mixed hearing loss, where both conductive and sensorineural components are present.
**Option C:** This option is incorrect because the "O" sign is not typically associated with a normal hearing test, where both air and bone conduction thresholds are within normal limits.

**Clinical Pearl / High-Yield Fact**
The "O" sign is a classic finding in otosclerosis, and it is often used as a diagnostic clue in patients with suspected middle ear pathology.

**Correct Answer: C.**