**Core Concept**
PAS (Periodic Acid-Schiff) staining is a histological technique used to detect polysaccharides, particularly glycogen, glycoproteins, and mucins, in tissues. It relies on the periodic acid oxidation of 1,2-glycol groups, which are then reacted with Schiff's reagent to produce a magenta-colored product.

**Why the Correct Answer is Right**
PAS staining is commonly used to identify structures rich in glycogen, such as liver cells, and mucins, such as those found in respiratory and gastrointestinal epithelium. The enzyme alpha-glucosidase is involved in the breakdown of glycogen, and PAS staining can be inhibited by the presence of alpha-glucosidase inhibitors, such as iodoacetate.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because PAS staining is indeed used to identify glycogen-containing structures.
**Option B:** Incorrect because PAS staining is used to identify mucins in respiratory and gastrointestinal epithelium.
**Option C:** Incorrect because PAS staining is used to identify glycogen-containing structures, such as liver cells.

**Clinical Pearl / High-Yield Fact**
PAS staining is particularly useful in the diagnosis of glycogen storage diseases, such as von Gierke's disease, where liver cells are filled with glycogen. Additionally, PAS staining can be used to identify malignant cells, which often have altered glycosylation patterns.

**Correct Answer:** A.