You are answering a USMLE-style medical question. Question: A 79-year-old woman comes to the physician for the evaluation of a 2-month history of a non-productive cough and fatigue. During this period, she also has had a 4.5-kg (10-lb) weight loss and has become increasingly short of breath with mild exertion. She has congestive heart failure and hypertension. Three months ago, she was in India for 3 weeks to attend a family wedding. She worked as a seamstress in a textile factory for 50 years. She has smoked one pack of cigarettes daily for 47 years. Her current medications include enalapril, digoxin, isosorbide, spironolactone, and metoprolol. She appears thin. Her temperature is 37.0°C (98.6°F), pulse is 90/min, respirations are 25/min, and blood pressure is 110/70 mm Hg. Pulse oximetry on room air shows an oxygen saturation of 94%. There is dullness to percussion and decreased breath sounds over the right lung base. The remainder of the examination shows no abnormalities. Laboratory studies show a glucose level of 90 mg/dL, serum lactate dehydrogenase of 227 U/L, and serum protein of 6.3 g/dL. An x-ray of the chest shows nodular pleural lesions on the right side and a moderate-sized pleural effusion. Thoracentesis shows 250 ml of turbid fluid. Analysis of the pleural fluid aspirate shows: Erythrocyte count 1/mm3 Leukocyte count 4,000/mm3 Glucose 59 mg/dl Lactate dehydrogenase 248 U/L Protein 3.8 g/dL Which of the following is the most likely underlying cause of this patient's effusion?" Options: A) Bronchial adenocarcinoma B) Mesothelioma C) Nephrotic syndrome D) Congestive heart failure Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.