You are answering a USMLE-style medical question. Question: A 62-year-old patient has been hospitalized for a week due to a stroke. One week into the hospitalization, he develops a fever and purulent cough. His vitals include: heart rate 88/min, respiratory rate 20/min, temperature 38.4°C (101.1°F), and blood pressure 110/85 mm Hg. On physical examination, he has basal crackles on the right side of the chest. Chest radiography shows a new consolidation on the same side. Complete blood count is as follows: Hemoglobin 16 mg/dL Hematocrit 50% Leukocyte count 8,900/mm3 Neutrophils 72% Bands 4% Eosinophils 2% Basophils 0% Lymphocytes 17% Monocytes 5% Platelet count 280,000/mm3 What is the most likely causal microorganism? Options: A) Streptococcus pneumoniae B) Mycobacterium tuberculosis C) Haemophilus influenzae D) Staphylococcus aureus Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.