You are answering a USMLE-style medical question. Question: A 46-year-old woman presents with a 5-month history of worsening dry cough, occasional shortness of breath, and fatigue. She says she is now having trouble walking a full block. For the past week, she also has noticed bilateral swelling of the lower legs. She denies chest pain, fever, chills, syncope, or bloody sputum. Current vitals include: temperature 37.0°C (98.6°F), pulse 63/min, blood pressure 128/91 mm Hg and respiratory rate 15/min. On physical examination, there is elevated jugular venous pressure, decreased breath sounds bilaterally at the lung bases, and 1+ non-pitting edema bilaterally in the lower extremities. A chest X-ray demonstrates a slightly enlarged cardiac silhouette. Which of the following is the most appropriate next step in the diagnosis of this patient? Options: A) Bronchoalveolar wash B) Pulmonary function studies C) Echocardiography D) Chest CT Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.