**Core Concept**
The aortic opening of the diaphragm is a crucial passage through which vital structures pass, facilitating the transition between the thoracic and abdominal cavities. It is a key landmark in the anatomy of the diaphragm, and knowledge of its contents is essential for medical professionals.

**Why the Correct Answer is Right**
The aortic opening of the diaphragm is a large, oval-shaped passage that allows for the passage of the aorta, the thoracic duct, and the azygos vein, among other structures. The aorta, in particular, is a major blood vessel that arises from the left ventricle of the heart and descends through the thoracic cavity, passing through the aortic opening of the diaphragm to enter the abdominal cavity. This passage is essential for maintaining blood circulation to the lower body.

**Why Each Wrong Option is Incorrect**
* **Option A:** The esophagus passes through the esophageal hiatus of the diaphragm, not the aortic opening. The esophageal hiatus is a separate, smaller opening that allows for the passage of the esophagus.
* **Option B:** The vena cava superior passes through the caval opening of the diaphragm, not the aortic opening. The caval opening is another distinct passage that allows for the passage of the superior vena cava.
* **Option C:** The phrenic nerves pass through the diaphragm but not through the aortic opening. The phrenic nerves are responsible for innervating the diaphragm and are found in the thoracic cavity, not in the abdominal cavity.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that the aortic opening of the diaphragm is the largest of the three main openings in the diaphragm, and it allows for the passage of the aorta, the thoracic duct, and the azygos vein. This knowledge is crucial for medical professionals to identify and manage various conditions, such as aortic aneurysms or thoracic duct injuries.

**Correct Answer:** D