You are answering a USMLE-style medical question. Question: A 70-year-old man presents with cough and progressively worsening shortness of breath for the last 6 months. He feels short of breath even without exertion and states he ‘got winded’ while walking to his bedroom last night. He describes his cough as non-productive and says he can identify no recognizable triggers. No significant past medical history. The patient is a retired welder and has been living with his son since his wife passed away 5 years ago. He denies any smoking history or current alcohol or drug use. His vital signs include: pulse rate 72/min, respiratory rate 15/min, blood pressure 134/80 mm Hg, and temperature 36.8°C (98.0°F). On physical examination, digital clubbing is noted. Bilateral basilar fine crackles on noted on pulmonary auscultation. Expiratory flow rates are measured and found to be high when corrected for lung volume. A chest X-ray is performed and shown in the image below. Which of the following most likely accounts for the increased expiratory flow rate in this patient? Options: A) Anatomical dead space B) Lung compliance C) Radial traction on airway wall D) Small airway wall thickness Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.