## Core Concept
The semicircular canals are part of the **vestibular system** in the inner ear, which is responsible for detecting changes in head position and movement. They are filled with a fluid called **endolymph** and are lined with hair cells that convert mechanical stimuli into electrical signals. The vestibular system helps maintain balance and spatial orientation.

## Why the Correct Answer is Right
The correct answer, , indicates that semicircular canals are stimulated by **rotational movements**. When the head rotates, the fluid in the semicircular canals lags behind due to inertia, bending the hair cells and triggering a signal. This signal is transmitted to the brain, which interprets it as rotation. The semicircular canals are specifically designed to detect angular acceleration, making them crucial for dynamic balance.

## Why Each Wrong Option is Incorrect
* **Option A:** - This option is incorrect because linear acceleration is detected by the **otolith organs** (utricle and saccule), not the semicircular canals.
* **Option B:** - This option is incorrect because, while changes in head position are indeed detected by the vestibular system, the specific role of detecting changes in head position is more closely associated with the otolith organs.
* **Option C:** - This option is incorrect because the detection of sound is the function of the **cochlea**, which is a different part of the inner ear.

## Clinical Pearl / High-Yield Fact
A key point to remember is that **benign paroxysmal positional vertigo (BPPV)** often involves the semicircular canals. BPPV is caused by the movement of otoconia (calcium carbonate crystals) within the inner ear, which can stimulate the hair cells in the semicircular canals, leading to brief but intense episodes of vertigo triggered by specific head movements.

## Correct Answer Line
**Correct Answer: D. rotational movements**