**Core Concept**
Xerophthalmia is a severe dryness of the conjunctiva and cornea caused by a deficiency in vitamin A. It is a hallmark of vitamin A deficiency (VAD) and can lead to corneal ulcers, blindness, and even death if left untreated.

**Why the Correct Answer is Right**
Vitamin A is essential for the health of the cornea and conjunctiva. A deficiency in vitamin A impairs the normal functioning of the mucous membranes, leading to a decrease in tear production and an increase in the risk of corneal ulcers. The primary cause of xerophthalmia is a lack of vitamin A in the diet, which can occur due to malnutrition, poor dietary habits, or conditions that impair vitamin A absorption.

**Why Each Wrong Option is Incorrect**
* **Option A:** Vit C deficiency is associated with scurvy, which presents with symptoms such as fatigue, malaise, and poor wound healing, but it is not directly linked to xerophthalmia.
* **Option B:** Small bowel resection can lead to malabsorption of various nutrients, including vitamin A, but it is not a direct cause of xerophthalmia.
* **Option C:** Cystic fibrosis is a genetic disorder that affects the respiratory, digestive, and reproductive systems, but it is not a primary cause of xerophthalmia.
* **Option D:** Chronic alcoholism can lead to malnutrition and impaired vitamin A absorption, but it is not a direct cause of xerophthalmia.
* **Option E:** Glomerulonephritis is a group of kidney disorders characterized by inflammation of the glomeruli, but it is not directly linked to xerophthalmia.

**Clinical Pearl / High-Yield Fact**
Vitamin A deficiency is a leading cause of preventable blindness worldwide. In areas where vitamin A deficiency is prevalent, supplementation with vitamin A can significantly reduce the risk of xerophthalmia and other related complications.

**Correct Answer: B. Small bowel resection can lead to malabsorption of vitamin A, but the primary cause of xerophthalmia is a direct deficiency of vitamin A.