This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: mycology, Subject name: Microbiology
[{'content': 'A farmer has an ulcer on a leg with indurated margin and multiple sinuses with discharging black granules. The likely diagnosis is \nSelect and explain. \nA. Mycetoma, B. Scrofuloderma, C. Lupus vulgaris, D. Actinomycosis', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Actinomycotic mycetoma - white to yellow granules and filaments are thin. Mycotic mycetoma - black granules and filaments are stout. Ref: Textbook of Microbiology, Ananthanarayan and Paniker; 9th edition', 'role': 'assistant'}]