An 8-year-old boy presents fever， headache and cough for 6 days. Chest X-ray shows cloudy infiltration. Mycoplasma antibody(MP-IgM) is 1 : 320. The diagnosis is

A: acute bronchitis
B: staphylococci aureus pneumonia
C: adenovirus pneumonia
D: respiratory syncytial virus pneumonia
E: mycoplasma pneumonial pneumonia

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