Q. A 62-year-old man with a history of chronic obstructive pulmonary disease (COPD) presents to the emergency department with increasing shortness of breath and cough over the past few days. He reports no fever, chest pain, or hemoptysis. On physical examination, his vital signs are as follows: temperature 98.6°F (37°C), blood pressure 140/90 mmHg, heart rate 110 beats/min, respiratory rate 28 breaths/min, and oxygen saturation 88% on room air. Lung examination reveals decreased breath sounds and dullness to percussion on the left side. Chest X-ray shows a moderate-sized left pleural effusion. Thoracentesis is performed, and fluid analysis reveals a protein level of 2.5 g/dL (serum protein level of 6.5 g/dL). What is the most likely type of pleural effusion?