This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Microbiology
[{'content': "The first sign of Vitamin A deficiency is \nSelect and explain. \nA. Conjunctival xerosis, B. Corneal ulcer, C. Keratomalacia, D. Bitot's spot", 'role': 'user'}, {'content': "Answer: A \nExplanation: Modified classification WHO (Xerophthalmia) XN: Night blindnessXIA: Conjunctival xerosis XIB: Bitot's spotsX2: Corneal xerosisX3A: Corneal ulceration/keratomalacia less than 1/3rd corneal surfaceX3B: Corneal ulceration/keratomalacia equal to or more than 1/3rd corneal surface XS: Corneal scarXF: Xerophthalmia fundus.", 'role': 'assistant'}]