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: Microbiology
[{'content': 'Ecthyma gangrenosum is caused by - \nSelect and explain. \nA. Pseudomonas, B. Streptococcus, C. Staphylococcus, D. H. influenzae', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]