**Core Concept**
The assessment of hearing loss in infants requires a non-invasive, objective measurement that can detect auditory function in newborns. This involves evaluating the auditory brainstem response (ABR) to sound stimuli. The ABR is a neurophysiological test that measures the electrical response of the auditory nerve and brainstem to auditory stimuli.

**Why the Correct Answer is Right**
Otoacoustic emissions (OAEs) testing is a non-invasive method used to assess the function of the cochlea and auditory nerve in infants. It involves the use of a probe placed in the ear canal to emit sound stimuli and measure the response. OAEs testing is the investigation of choice in assessing hearing loss in infants due to its ease of use, low cost, and high sensitivity. The test can detect hearing loss in both ears simultaneously and can be performed on sleeping or awake infants. OAEs testing is often used as a screening tool to identify infants at risk for hearing loss.

**Why Each Wrong Option is Incorrect**
**Option A:** Auditory brainstem response (ABR) is an objective measurement of the auditory nerve and brainstem response to auditory stimuli, but it is typically used in infants who have failed OAEs testing or have a history of hearing loss. It requires sedation and is more expensive than OAEs testing.
**Option B:** Tympanometry measures the movement of the eardrum and middle ear function but does not assess the function of the cochlea or auditory nerve.
**Option C:** Rinne's test assesses the difference in bone and air conduction, but it is not a quantitative measurement and is not suitable for infants.

**Clinical Pearl / High-Yield Fact**
OAEs testing is a valuable tool in identifying infants at risk for hearing loss. It is essential to perform OAEs testing in all newborns before discharge from the hospital to ensure early detection and intervention.

**Correct Answer: C. Tympanometry measures the movement of the eardrum and middle ear function but does not assess the function of the cochlea or auditory nerve.**