## Core Concept
The question pertains to the identification of a specific type of gastritis, chronic antral gastritis, which is often associated with Helicobacter pylori infection. The staining method used to detect H. pylori in gastric biopsy specimens is crucial for diagnosis.

## Why the Correct Answer is Right
The correct answer, **Giemsa stain**, is used to stain the specimen because it is effective in highlighting the presence of Helicobacter pylori bacteria in gastric biopsy samples. Giemsa stain is a differential stain that can identify the characteristic spiral-shaped bacteria. H. pylori infection is a common cause of chronic gastritis, particularly in the antral region of the stomach.

## Why Each Wrong Option is Incorrect
- **Option A:** Warthin-Starry stain is indeed used to detect H. pylori but is less commonly used compared to Giemsa stain for this purpose. However, this option might seem plausible but is not the best answer here.
- **Option B:** Alcian blue is used to stain mucins and is not specifically used for detecting H. pylori.
- **Option D:** PAS (Periodic Acid-Schiff) stain is used to detect polysaccharides such as glycogen, and glycolipids in tissues, not for H. pylori.

## Clinical Pearl / High-Yield Fact
A key point to remember is that **Giemsa stain** is one of the preferred stains for detecting H. pylori in endoscopic biopsy specimens. The presence of H. pylori is a critical factor in the management of peptic ulcer disease and chronic gastritis, as it often necessitates antibiotic therapy.

## Correct Answer Line
**Correct Answer: C. Giemsa stain**