**Core Concept**
The aortic opening, also known as the aortic hiatus, is an opening in the diaphragm that allows certain structures to pass through between the thoracic and abdominal cavities. This opening is a critical anatomical landmark that plays a significant role in the passage of various structures.

**Why the Correct Answer is Right**
The vagus nerve is a vital cranial nerve that originates from the brainstem and extends down to the abdomen. However, unlike other structures that pass through the aortic opening, the vagus nerve does not traverse this opening. Instead, it passes through the esophageal hiatus, which is a separate opening in the diaphragm located near the aortic opening. The vagus nerve is responsible for various functions, including regulating the heart rate, facilitating peristalsis in the digestive tract, and controlling the parasympathetic nervous system.

**Why Each Wrong Option is Incorrect**
**Option A:** The aorta, being the largest artery in the body, does pass through the aortic opening, which allows it to ascend from the abdominal cavity into the thoracic cavity.

**Option C:** The azygos vein is a significant vein that passes through the aortic opening, allowing it to drain blood from the posterior walls of the thorax and abdomen into the superior vena cava.

**Option D:** The thoracic duct, which is the main lymphatic vessel in the body, also passes through the aortic opening, allowing it to drain lymph from the body into the bloodstream.

**Clinical Pearl / High-Yield Fact**
It is essential for medical professionals to be aware of the anatomical structures that pass through the aortic opening and the esophageal hiatus, as knowledge of these structures is crucial for understanding various clinical conditions, such as diaphragmatic hernias and thoracic outlet syndrome.

**✓ Correct Answer: B. B) Vagus nerve**