**Core Concept**
Fungal stains are essential in histopathology for the identification of fungi in tissue biopsy sections. They help in diagnosing various fungal infections, such as aspergillosis and histoplasmosis. The correct fungal stain should be able to differentiate fungi from other tissue components.

**Why the Correct Answer is Right**
The correct answer is Gomori's methenamine silver (GMS) stain. GMS stain is a widely used method for staining fungi in tissue biopsy sections. It works by reacting with the chitin in the fungal cell walls, producing a black precipitate that is visible under the microscope. This allows for the identification of fungi, including Aspergillus, Candida, and Histoplasma. The GMS stain is particularly useful in diagnosing invasive aspergillosis and histoplasmosis.

**Why Each Wrong Option is Incorrect**
**Option A:** H&E stain is a general-purpose stain used in histopathology, but it is not specific for fungi. It stains the nuclei and cytoplasm of cells, but it does not react with fungal cell walls.
**Option B:** PAS stain (Periodic Acid-Schiff) is used to stain glycogen and other carbohydrates, but it is not specific for fungi. While it can stain some fungal elements, it is not as sensitive as GMS stain for fungal identification.
**Option C:** Gram stain is used to differentiate between gram-positive and gram-negative bacteria, but it is not used for fungal staining.

**Clinical Pearl / High-Yield Fact**
GMS stain is a critical tool in the diagnosis of invasive fungal infections, particularly in immunocompromised patients. It is essential to consider fungal infections in patients with severe immunosuppression, particularly those with neutropenia or on long-term corticosteroids.

**Correct Answer:** C. Gomori's methenamine silver (GMS) stain.