**Core Concept**
The posterior cardinal vein is a major embryonic structure that ultimately gives rise to several significant venous pathways in the adult. During embryonic development, the posterior cardinal veins play a crucial role in the formation of the venous system.

**Why the Correct Answer is Right**
The posterior cardinal veins are a pair of major veins that develop in the embryo, and they eventually regress and give rise to various parts of the venous system. The left posterior cardinal vein primarily contributes to the formation of the left common iliac vein, which is a major vein that drains blood from the lower limbs and the pelvic region. The common iliac vein is formed by the fusion of the left and right common iliac veins, but in this context, we are focusing on the left posterior cardinal vein's contribution.

**Why Each Wrong Option is Incorrect**
**Option A:** The superior vena cava is formed by the regression of the anterior cardinal veins, not the posterior cardinal veins. The anterior cardinal veins give rise to the superior vena cava through a series of complex transformations during embryonic development.
**Option B:** The internal jugular vein is also formed from the anterior cardinal veins, which are distinct from the posterior cardinal veins. The internal jugular veins are responsible for draining blood from the head and neck region.
**Option C:** The external jugular vein is formed from the anterior cardinal veins as well. It is a superficial vein located on the lateral aspect of the neck and plays a minor role in venous drainage compared to the internal jugular vein.
**Option D:** While the common iliac vein is indeed related to the posterior cardinal veins, the right posterior cardinal vein contributes to the formation of the right common iliac vein, not the left. The correct answer focuses on the left posterior cardinal vein's contribution.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that the venous system develops from multiple embryonic structures, including the anterior cardinal veins, posterior cardinal veins, and common cardinal veins. Understanding the embryonic origins of these veins can help in identifying potential anomalies and variations in the adult venous system.

✓ Correct Answer: D. Common iliac vein