This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Biological Materials & Stains, Subject name: Forensic Medicine
[{'content': 'ABO antigens are not found in: \nSelect and explain. \nA. Semen, B. Plasma, C. Sweat, D. CSF', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Ans: D (CSF) Ref: The Essentials of Forensic Medicine and Toxicology by KS Narayan Reddy. 29th edition. 2010Explanation:ABO antigensABO antigens are found in high concentration in saliva, semen, vaginal and gastric secretions.They are found in low titres in sweat, tears and urine.Totally absent in nerve tissue, epithelium, skin appendages, bone and cartilage.', 'role': 'assistant'}]