**Core Concept**
The semicircular canals are a part of the vestibular system in the inner ear, responsible for detecting rotational movements and maintaining balance. They contain sensory hair cells that respond to changes in fluid movement within the canals, which is triggered by rotational stimuli.

**Why the Correct Answer is Right**
The semicircular canals are stimulated by rotation because they contain fluid-filled canals that are lined with sensory hair cells. When the head rotates, the fluid within the canals lags behind due to inertia, causing the hair cells to bend and trigger a signal to the brain. This signal is transmitted through the vestibulocochlear nerve (cranial nerve VIII) and processed in the vestibular nuclei of the brainstem. The vestibular system uses this information to maintain balance and orientation during rotational movements.

**Why Each Wrong Option is Incorrect**
**Option A:** Gravity stimulates the otolith organs (utricle and saccule), not the semicircular canals. The otolith organs detect linear acceleration and changes in head position relative to gravity.

**Option B:** Linear acceleration stimulates the otolith organs (utricle and saccule), not the semicircular canals. The otolith organs detect changes in linear acceleration and head position relative to gravity.

**Option D:** Sound stimulates the cochlea, not the semicircular canals. The cochlea is responsible for detecting sound vibrations and transmitting them to the brain as sound.

**Clinical Pearl / High-Yield Fact**
The vestibular system is responsible for maintaining balance and orientation during rotational movements. Damage to the semicircular canals or the vestibular nerve can lead to vestibular disorders such as vertigo, dizziness, and balance problems.

✓ Correct Answer: C. Rotation. Rotation stimulates the semicircular canals, which are responsible for detecting rotational movements and maintaining balance.