This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Bacterial infection, Subject name: Medicine
[{'content': 'There is no correlation between X-ray appearance and clinical state of the patient with pneumonia in: \nSelect and explain. \nA. Mycoplasma, B. Freidlanders, C. Pneumococcal, D. Staphylococcal', 'role': 'user'}, {'content': "Answer: A \nExplanation: Mycoplasma infection may begin with a sore throat and the most common presenting symptom is cough. The possibility of M. pneumoniae- when community-acquired pneumonia fails to respond to treatment with a penicillin or a cephalosporin--antibiotics that are ineffective against mycoplasmas. Clinical findings, non-microbiologic laboratory tests, and chest radiography are not useful for differentiating M. pneumoniae pneumonia from other types of community- acquired pneumonia. In addition, since M. pneumoniae lacks a cell wall, it is not visible on gram's stain.", 'role': 'assistant'}]