**Core Concept**
Erythema nodosum is a type of skin inflammation characterized by the formation of tender, red nodules or lesions, typically on the lower legs. This condition is often associated with various underlying causes, including infections, autoimmune diseases, and medications.

**Why the Correct Answer is Right**
Erythema nodosum is a hypersensitivity reaction to an antigen, leading to inflammation in the subcutaneous fat, fascia, and skin. The exact pathogenesis is not fully understood, but it is thought to involve the activation of immune cells, such as T lymphocytes and macrophages, in response to an antigen. This results in the release of pro-inflammatory cytokines and chemokines, which attract more immune cells to the affected area, causing the characteristic skin lesions.

**Why Each Wrong Option is Incorrect**
**Option A:** This option would require more information about the specific cause of erythema nodosum. Without more context, we cannot determine its accuracy.
**Option B:** This option is not a cause of erythema nodosum. While tuberculosis can cause skin lesions, it is not typically associated with erythema nodosum. Other conditions, such as sarcoidosis or lymphoma, may be more likely to cause skin lesions in this context.
**Option C:** This option is a common cause of erythema nodosum. Sarcoidosis is a systemic granulomatous disease that can affect multiple organs, including the skin, lungs, and lymph nodes. It is a known cause of erythema nodosum.

**Clinical Pearl / High-Yield Fact**
It's essential to consider the patient's overall clinical context when evaluating erythema nodosum, as it can be a manifestation of an underlying systemic disease. A thorough medical history and physical examination can help identify potential causes and guide further diagnostic testing.

**Correct Answer:** C. Sarcoidosis