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: Pathology
[{'content': 'Although more than 400 blood groups have been identified,the ABO blood group system remians the mostimpoant in clinical medicne because : \nSelect and explain. \nA. It was the first blood group system to be discovered, B. It has four different blood groups A,B, AB, O (H)., C. ABO(H) antigens are present in most body tissues and fluids., D. ABO(H) antibodies are invariably present in plasma when persons RBC lacks the corresponding antigen', 'role': 'user'}, {'content': 'Answer: D \nExplanation: . ABO(H) antibodies are invariably present in plasma when persons RBC lacks the corresponding antigen', 'role': 'assistant'}]