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 24-year-old male presents to a STD clinic with a single painless ulcer on external genitalia. The choice of laboratory test to look for the etiological agent would be – \nSelect and explain. \nA. Scrappings from ulcer for culture on chocolate agar with antibiotic supplement, B. Serology from detection of specific IgM antibodies, C. Scrappings from ulcer for dark field microscopy, D. Scrappings from ulcer for tissue culture', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Clues are:-\n\n\nPainless ulcer\nSingle lesion\n\n\nIt may be either LGV or chance:-\n\nChancre \xa0→ Darkfield microscopy or serological tests (VDRL, FTA-ABS).\nIGV\xa0→ Demonstration of inclusion bodies, fries test, CFT.\n\nAmongst all these tests only darkfield microscopy has been given in the options.\nSo, I am assuming that it is a case of primary syphilis (chancre), for which dark field microscopy can be used for diagnosis.', 'role': 'assistant'}]