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
1st clinical sign of vitamin A deficiency is 
Select and explain. 
A. night blindness, B. bitot's spots, C. xerostomia, D. conjunctival xerosis
D: conjunctival xerosis
Answer: D: conjunctival xerosis 
Explanation: Night blindness (nyctalopia) is  one  of  the  earliest symptoms  of  vitamin  A  deficiency.