**Core Concept**
The Glasgow Coma Scale (GCS) is a neurological scale used to assess the level of consciousness in a person after a brain injury. It consists of three parameters: eye opening, verbal response, and motor response, which are used to calculate a total score that can indicate the severity of brain injury.

**Why the Correct Answer is Right**
The GCS is a widely used tool for assessing patients with altered mental status, and its parameters are well-established in medical literature. The three parameters of the GCS are eye opening, verbal response, and motor response. These parameters are used to assess the level of consciousness in a patient and are crucial in guiding treatment decisions.

**Why Each Wrong Option is Incorrect**
* **Option A:** Eye opening is one of the parameters of the GCS, so this option is incorrect.
* **Option B:** Verbal response is another parameter of the GCS, so this option is incorrect.
* **Option D:** Motor response is also a parameter of the GCS, so this option is incorrect.

**Clinical Pearl / High-Yield Fact**
The GCS is a sensitive tool for assessing patients with brain injuries, and its parameters should be assessed carefully to determine the severity of the injury. A score of 3-8 is considered severe brain injury, while a score of 9-12 is considered moderate, and a score of 13-15 is considered mild.

**Correct Answer: C.**