You are answering a USMLE-style medical question. Question: Twelve hours after admission to the hospital because of a high-grade fever for 3 days, a 15-year-old boy has shortness of breath. During this period, he has had generalized malaise and a cough productive of moderate amounts of green sputum. For the past 10 days, he has had fever, a sore throat, and generalized aches; these symptoms initially improved, but worsened again over the past 5 days. His temperature is 38.7°C (101.7°F), pulse is 109/min, respirations are 27/min, and blood pressure is 100/70 mm Hg. Pulse oximetry on room air shows an oxygen saturation of 93%. There are decreased breath sounds and crackles heard over the upper right lung field. His hemoglobin concentration is 13.3 g/dL, leukocyte count is 15,000/mm3, and platelet count is 289,000/mm3. An x-ray of the chest shows a right upper-lobe infiltrate. Which of the following is the most likely cause of this patient's symptoms? Options: A) Streptococcus pneumoniae B) Mycoplasma pneumoniae C) Chlamydophila pneumoniae D) Haemophilus influenzae Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.