**Core Concept**
The question pertains to the neural mechanisms underlying skilled voluntary movements, specifically the initial activation of motor centers in the brain. The correct answer is related to the primary motor cortex and its role in initiating voluntary movements.

**Why the Correct Answer is Right**
The primary motor cortex is the first center to get activated before the onset of skilled voluntary movements. This area is responsible for transmitting signals to the spinal cord and brainstem, which then coordinate the movement. The primary motor cortex receives input from the precentral gyrus and sends output to the pyramidal tracts, which are crucial for executing voluntary movements. The activation of the primary motor cortex is a critical step in the motor control process, allowing for the precise and coordinated movement of muscles.

**Why Each Wrong Option is Incorrect**
* **Option A:** The premotor cortex is involved in planning and coordinating movements, but it is not the first center to get activated before the onset of skilled voluntary movements.
* **Option B:** The supplementary motor area is involved in the planning and execution of complex movements, but it is not the initial center to get activated.
* **Option C:** The cerebellum plays a crucial role in the coordination and regulation of movements, but it is not the first center to get activated before the onset of skilled voluntary movements.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the primary motor cortex is responsible for transmitting signals to the spinal cord and brainstem, which then coordinate the movement. This understanding is crucial for diagnosing and managing motor disorders, such as stroke or spinal cord injuries.

**Correct Answer: A. Primary motor cortex**