This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
Keratinising metaplasia of salivary glands results due to deficiency of 
Select and explain. 
A. Vitamin A, B. Thiamine, C. Riboflavin, D. Vitamin E
A: Vitamin A
Answer: A: Vitamin A 
Explanation: Vitamin A deficiency produces keratinizing metaplasia of the normally columnar ductal epithelium in the major and minor salivary glands.
Ref : Handbook of Experimental  Stomatology,edited by Samuel Dreizen, Barnet M. Levy.