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': 'Prostate specific antigen is used as \nSelect and explain. \nA. Tumor marker, B. Proto oncogene, C. Oncogene, D. Bacterial antigen', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]