**Core Concept**
The question is testing the association between specific nutritional deficiencies and disorders of salivary gland hyperplasia and keratinization. This involves understanding the role of essential nutrients in maintaining salivary gland function and structure.

**Why the Correct Answer is Right**
The correct answer is associated with disorders of salivary gland hyperplasia and keratinization due to its role in maintaining epithelial cell integrity and function. The correct answer is a B-vitamin that plays a crucial role in maintaining the health of epithelial cells, including those in the salivary glands. Deficiency in this vitamin can lead to abnormalities in keratinization and hyperplasia of the salivary glands.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is not directly associated with the maintenance of epithelial cell function and structure. While it is an essential nutrient, its deficiency is more commonly associated with other systemic disorders.
**Option B:** This option is incorrect because it is not directly linked to keratinization and hyperplasia of the salivary glands. Its deficiency is more commonly associated with disorders of the nervous system.
**Option C:** This option is incorrect because it is not the primary vitamin associated with maintaining epithelial cell integrity and function.

**Clinical Pearl / High-Yield Fact**
Deficiency in the correct B-vitamin can lead to a range of systemic disorders, including neurological and dermatological conditions. It is essential for postgraduate medical students to recognize the role of this vitamin in maintaining epithelial cell function and structure.

**Correct Answer:** A. Riboflavin