This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: S.T.D., Subject name: Skin
[{'content': 'Chancroid is caused by ? \nSelect and explain. \nA. H. Ducrei, B. N. Gonnorrhea, C. T. Pallidum, D. H. Influenza', 'role': 'user'}, {'content': 'Answer: A \nExplanation: ANSWER: (A) H. Ducrei REF: Roxburgh\'s Common Skin Diseases p. 102 Repeat in June 2010 See APPENDIX-47 below for list of "STD\'s" 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'}]