This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: G.I.T, Subject name: Physiology
[{'content': 'ABO antigens are present in all except \nSelect and explain. \nA. Sweat, B. Saliva, C. Semen, D. CSF', 'role': 'user'}, {'content': 'Answer: D \nExplanation: in ABH antigents are absent in CSF Ref: guyton and hall textbook of medical physiology 12 edition page number:813,814,815', 'role': 'assistant'}]