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: Social & Preventive Medicine
[{'content': 'What is deficient in exclusively breast fed baby? \nSelect and explain. \nA. Vitamin B, B. Vitamin A, C. Vitamin C, D. Proteins', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is 'a' i.e., Vitamin B o Deficiency of Vitamin B12 may occur in exclusive breastfed infants of mother who is on strict vegetarian diet.", 'role': 'assistant'}]