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
[{'content': 'Xerophthalmia is caused by: \nSelect and explain. \nA. Vitamin A deficiency, B. Vitamin D deficiency, C. Vitamin C deficiency, D. Vitamin K deficiency', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]