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: Unknown
[{'content': 'The first sign of Vit A deficiency is : \nSelect and explain. \nA. Conjunctiva xerosis, B. Corneal ulcer, C. Keratomalacia, D. Bitot’s spot', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Modified classification WHO (Xerophthalmia) XN : Night blindness\nXIA : Conjunctival xerosis XIB : Bitot’s spots\nX2: Corneal xerosis\nX3A : Corneal ulceration/keratomalacia less than 1/3rd corneal surface\nX3B : Corneal ulceration/keratomalacia equal to or more than 1/3rd corneal surface XS : Corneal scar\nXF : Xerophthalmia fundus.', 'role': 'assistant'}]