**Core Concept**
Farmer's Lung is a type of hypersensitivity pneumonitis, a lung disease caused by an immune system reaction to inhaled particles. This condition is characterized by an abnormal immune response to certain antigens, leading to inflammation and damage in the lungs.

**Why the Correct Answer is Right**
Farmer's Lung is primarily caused by exposure to thermophilic actinomycetes, a type of bacteria found in moldy hay, grain, or other crop products. When these bacteria are inhaled, they trigger an immune response, leading to inflammation and damage in the lungs. The condition is often seen in agricultural workers who handle moldy hay or grain. The immune system reacts to the inhaled particles, releasing cytokines and other chemical mediators that cause inflammation and damage to the lung tissue.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Aspergillus is a type of fungus that can cause other types of lung infections, such as aspergillosis, but it is not the primary cause of Farmer's Lung.
**Option B:** This option is incorrect because Histoplasma capsulatum is a type of fungus that causes histoplasmosis, a different type of lung infection.
**Option C:** This option is incorrect because Pseudomonas aeruginosa is a type of bacteria that can cause various types of infections, but it is not associated with Farmer's Lung.

**Clinical Pearl / High-Yield Fact**
Farmer's Lung is a classic example of an occupational lung disease, highlighting the importance of proper ventilation and protective gear in agricultural settings to prevent exposure to moldy hay and grain.

**Correct Answer:**
(You need to provide the correct answer options)