**Core Concept**
Ghons focus refers to the primary complex of tuberculosis, which is the initial lesion formed by the Mycobacterium tuberculosis bacteria in the human body. It is characterized by a granulomatous reaction, involving the fusion of macrophages, lymphocytes, and other immune cells to form a granuloma.

**Why the Correct Answer is Right**
The primary complex of tuberculosis, also known as Ghons focus, typically involves the lung parenchyma and the hilar lymph nodes. The bacteria enter the body through inhalation, and the initial lesion is formed in the lung parenchyma. The immune response to the bacteria leads to the formation of a granuloma, which is a characteristic feature of tuberculosis. The granuloma consists of a central area of caseous necrosis, surrounded by a rim of epithelioid cells, lymphocytes, and macrophages. The hilar lymph nodes become involved due to the spread of the bacteria through the lymphatic system.

**Why Each Wrong Option is Incorrect**
**Option A:** Ghons focus is not typically seen in the pleura.
* Ghons focus is usually associated with the lung parenchyma and the hilar lymph nodes, rather than the pleura.

**Option B:** Ghons focus is not a characteristic feature of pulmonary embolism.
* Ghons focus is a specific type of granuloma associated with tuberculosis, whereas pulmonary embolism is a condition characterized by the blockage of a pulmonary artery by a blood clot.

**Option C:** Ghons focus is not a type of lung cancer.
* Ghons focus is a granulomatous reaction to tuberculosis, whereas lung cancer refers to a malignancy of the lung tissue.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that Ghons focus is a key feature of primary tuberculosis, and its identification is crucial for diagnosing this condition. The presence of a Ghons focus can be confirmed through imaging studies, such as chest X-rays or CT scans, and histopathological examination of tissue samples.

**Correct Answer: C. Primary tuberculosis.