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
Blood group antigen NAG transferase present but galactosyl transferase is absent is ? 
Select and explain. 
A. Group A, B. Group B, C. Group AB, D. Group 0
A: Group A
Answer: A: Group A 
Explanation: Ans. is'a'i.e., Group AABO gene products are the products of enzymatic reactions, catalysed by enzymes called glycosyltransferase (galactosyltransferase).