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: Dental
[{'content': 'A 26 year old male with recent history of unprotected sexual intercourse comes to opd with complaints of painless, indurated ulcer over the glans which exuded clear serum. Bilateral painless inguinal lymphadenopathy is also present. The most appropriate diagnostic test is: \nSelect and explain. \nA. Gram stain of ulcer discharge, B. ELISA for HIV infection, C. Dark ground microscopy of ulcer discharge, D. Giemsa stain of lymph node aspirate', 'role': 'user'}, {'content': 'Answer: C \nExplanation: History of sexual intercourse, painless and hard ulcer (chancre) and painless inguinal lymphadenopathy is suggestive of primary syphilis.\nDark ground examination is done to demonstrate spirochetes.', 'role': 'assistant'}]