Explanation:

- Xerophthalmia is a condition characterized by dry eyes and is often linked to a deficiency in a specific vitamin.

- It is primarily caused by a deficiency of vitamin A, which is crucial for maintaining proper vision and eye health.

- Option 1: Vitamin D - Essential for bone health, not directly related to xerophthalmia.

- Option 2: Vitamin C - Important for skin and immune health, not directly related to xerophthalmia.

- Option 3: Vitamin A - Correct! It plays a key role in maintaining healthy vision and preventing xerophthalmia.

- Option 4: Vitamin K - Necessary for blood clotting, not directly related to xerophthalmia.