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: Ophthalmology
[{'content': 'Earliest feature of vitamin deficiency is: \nSelect and explain. \nA. Conjunctival xerosis, B. Nyctalopia, C. Retinopa thy, D. Pain', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Conjunctival xerosis', 'role': 'assistant'}]