**Core Concept:** Tuberculosis (TB) is an infectious disease primarily caused by the bacteria Mycobacterium tuberculosis. It primarily affects the lungs, called pulmonary TB, but can also affect other organs, called extrapulmonary TB.

**Why the Correct Answer is Right:** Pulmonary TB is the most common presentation of TB, affecting the lungs. When the bacteria enters the body, it predominantly targets the alveoli, causing inflammation and tissue damage. The immune response to the infection leads to the formation of granulomas, which are clusters of immune cells attempting to control the infection. If the immune system fails to control the infection, the bacteria can disseminate to other organs, leading to extrapulmonary TB.

**Why Each Wrong Option is Incorrect:**

A. **Option A (Liver):** Though TB can involve the liver, it is less common compared to pulmonary TB.

B. **Option B (Muscles):** Extrapulmonary TB can involve muscles, but it is not the most common site of involvement.

C. **Option C (Bones):** While TB can affect bones, it is still less common than pulmonary TB.

D. **Option D (Central Nervous System):** Although TB can involve the central nervous system, it is less common than pulmonary TB in the majority of cases.

**Clinical Pearl:** It is essential for medical students and practitioners to understand the clinical presentation of TB, as proper diagnosis and treatment can significantly reduce morbidity and mortality. Pulmonary TB is the most common and easily diagnosable form, while extrapulmonary TB poses diagnostic challenges due to varied clinical presentation and less direct involvement of pathogens.

**Correct Answer:** **Option D (Central Nervous System):** TB can involve the central nervous system (CNS) and is more common in immunocompromised individuals, such as those with HIV or on corticosteroid therapy. Involvement of CNS can lead to meningitis, tuberculomas, and miliary tuberculosis. However, this is not the most common site of TB involvement, which is pulmonary TB.