**Core Concept**
The **common carotid artery** is a major artery that supplies blood to the head and neck. It bifurcates into two main branches, supplying the brain and face. This bifurcation occurs at a specific level in the neck.

**Why the Correct Answer is Right**
The common carotid artery bifurcates into the **internal carotid artery** and **external carotid artery** at the level of the **upper border of the thyroid cartilage**, which is around the C4 vertebra. This bifurcation is a crucial anatomical landmark.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately represent the level of bifurcation.
**Option B:** This option is also incorrect as it does not correspond to the correct anatomical level.
**Option D:** This option is incorrect because the bifurcation does not occur at this level.

**Clinical Pearl / High-Yield Fact**
The **common carotid artery bifurcation** is a key landmark for surgical and diagnostic procedures in the neck.

**Correct Answer:** C. At the level of upper border of thyroid cartilage