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: Skin
[{'content': 'Chancroid is caused by? \nSelect and explain. \nA. H. Ducrei, B. N. Gonnorrea, C. T. Pallidum, D. H. Influenza', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans:A.)H. Ducrei CHANCROID (SOFT SORE) This venereal infection is caused by the Gram-negative bacillus Haemophilus ducreyi. One to 5 days post-infection, a soft sloughy ulcer appears on the penis or vulva. The treatment of choice is erythromycin (500 mg 6-hourly for 14 days).', 'role': 'assistant'}]