Assignment task: By what mechanism does Vitamin A deficiency cause xerophthalmia?
1. By preventing the differentiation of newly-formed epithelial cells into mucus-secreting cells.
2. By preventing the differentiation of keratin-containing cells into antibody-secreting cells.
3. By increasing the differentiation of keratin-containing cells into mucus-secreting cells.
4. By reducing the formation of keratin-containing cells.