**Core Concept**
The occipital triangle is an anatomical region in the posterior aspect of the neck, bounded by the sternocleidomastoid muscle, the trapezius muscle, and the ligamentum nuchae. It contains vital structures related to the cervical spine and the scalp.

**Why the Correct Answer is Right**
The occipital triangle is a clinically significant region due to its proximity to the cervical spine and the scalp. It contains the occipital artery, which is a branch of the external carotid artery, and the greater occipital nerve, which is a branch of the dorsal ramus of the C2 spinal nerve. These structures provide blood supply and sensory innervation to the scalp, respectively.

**Why Each Wrong Option is Incorrect**
**Option A:** The subclavian artery is not typically considered a content of the occipital triangle. It is a major artery located in the thoracic cavity and is not directly related to the structures within this region.
**Option B:** The greater occipital nerve is indeed a content of the occipital triangle, making this option incorrect.
**Option C:** The lesser occipital nerve is also a content of the occipital triangle, making this option incorrect.

**Clinical Pearl / High-Yield Fact**
The occipital triangle is an important landmark in the posterior aspect of the neck, and its contents are relevant to both surgical and clinical practice. A thorough knowledge of the structures within this region is essential for accurate diagnosis and treatment.

**Correct Answer: A. The subclavian artery.**