**Core Concept**
The post-mortem examination involves a series of steps to assess the body's external and internal features. The sequence of opening body cavities is crucial to prevent contamination and ensure a thorough examination. The first body cavity to be opened is a matter of debate, but it generally involves the one that provides the most valuable information.

**Why the Correct Answer is Right**
The correct answer is the chest cavity. This is because the chest cavity contains vital organs such as the heart, lungs, and major blood vessels. The examination of these organs is essential to determine the cause of death, especially in cases of cardiac or respiratory failure. Opening the chest cavity first allows the examiner to assess the heart's condition, including any signs of trauma, disease, or previous medical interventions.

**Why Each Wrong Option is Incorrect**
* **Option A:** The abdominal cavity is not opened first because it contains organs that are less critical to the initial assessment of death. The abdominal organs are often examined later in the process.
* **Option B:** The pelvic cavity is not opened first because it contains organs that are not directly related to the primary cause of death. The pelvic organs are examined later in the process.
* **Option C:** The head cavity is not opened first because it requires specialized techniques and equipment to examine the brain and its contents. The head cavity is often examined later in the process.

**Clinical Pearl / High-Yield Fact**
When performing a post-mortem examination, it is essential to follow a standardized sequence to ensure a thorough and accurate assessment. The chest cavity is typically opened first, followed by the abdominal and pelvic cavities.

**Correct Answer: C. Chest cavity**