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: Physiology
[{'content': 'Blood group antigen NAG transferase present but galactosyl transferase is absent is ? \nSelect and explain. \nA. Group A, B. Group B, C. Group AB, D. Group 0', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is'a'i.e., Group AABO gene products are the products of enzymatic reactions, catalysed by enzymes called glycosyltransferase (galactosyltransferase).", 'role': 'assistant'}]