Normal hearing:
**Core Concept**
Auditory threshold is the minimum sound intensity required for a person to perceive a sound. Normal hearing is typically defined as the ability to detect sounds within a specific range of frequencies, usually between 20 Hz and 20,000 Hz.
**Why the Correct Answer is Right**
Normal hearing is characterized by the presence of functioning hair cells in the cochlea, particularly the outer hair cells, which are responsible for amplifying sound vibrations. The basilar membrane, a critical structure in the cochlea, plays a crucial role in sound processing and frequency analysis. In individuals with normal hearing, the auditory nerve transmits signals to the brain, allowing for the perception of sound.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is likely incorrect as it does not provide a clear definition of normal hearing.
**Option B:** This option might be incorrect as it does not specify the frequency range for normal hearing.
**Option C:** This option is incorrect because it refers to a condition where hearing is impaired, not normal.
**Clinical Pearl / High-Yield Fact**
A person with normal hearing can detect sounds with frequencies as low as 20 Hz and as high as 20,000 Hz, which is essential for everyday communication and overall auditory function.
**Correct Answer:** D