**Core Concept**
The question is testing the understanding of the mechanism of asphyxia, specifically the effect of external pressure on the airway. Asphyxia can occur due to various reasons, including obstruction of the airway, which can be caused by external pressure on the neck and chest.

**Why the Correct Answer is Right**
When external pressure is applied to the neck and chest, it can compress the thoracic cavity and prevent the lungs from expanding, leading to asphyxia. This is because the diaphragm and intercostal muscles are unable to contract effectively due to the external pressure, resulting in impaired gas exchange. The internal air passage, specifically the trachea, can become compressed, further restricting airflow.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it does not describe the correct mechanism of asphyxia due to external pressure on the neck and chest.

**Option B:** This option is incorrect as it refers to a different type of asphyxia, where the internal air passage is blocked by a foreign object, rather than external pressure.

**Option C:** This option is incorrect as it refers to a different type of asphyxia, where the airway is blocked due to a foreign object or swelling, rather than external pressure.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that asphyxia can occur due to various mechanisms, and it's crucial to identify the underlying cause to provide appropriate treatment. In cases of suspected asphyxia due to external pressure, it's essential to relieve the pressure immediately to restore airflow.

**Correct Answer: D. Strangulation.**