**Core Concept**
The Glascow Coma Scale (GCS) is a neurological scale used to assess the level of consciousness in a patient. It is a widely used tool in the assessment of head injuries and other conditions that affect the brain. The GCS evaluates three aspects of a patient's neurological status: eye opening, verbal response, and motor response.

**Why the Correct Answer is Right**
To calculate the GCS score, the patient's responses to verbal commands, pain, and motor function are evaluated. In this case, the patient opens his eyes to pain (score of 2), does not speak but moans (verbal response of 1), and has a motor response to pain in the left limb (score of 3). The right limb does not move, but this is not evaluated as it is an extended posture, not a flexion response (score of 0). The GCS score is the sum of the scores for eye opening, verbal response, and motor response.

* Eye opening: 2 (opens to pain)
* Verbal response: 1 (moans)
* Motor response: 3 (moves limb to pain)

GCS score = 2 + 1 + 3 = 6

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not provided.
* **Option B:** This option is not provided.
* **Option C:** This option is not provided.
* **Option D:** This option is not provided.

**Clinical Pearl / High-Yield Fact**
The GCS score is a crucial tool for assessing the severity of head injuries and guiding treatment. A score of 8 or less indicates a severe head injury, while a score of 9-12 indicates a moderate head injury. The GCS score has been shown to be a reliable predictor of outcome in patients with head injuries.

**Correct Answer:** 6. The patient's GCS score is 6.