A 55-year-old man with a 3-year history of sarcoidosis presents to clinic with progressive dyspnea on exertion over the past 6 months. He denies fever, night sweats, or weight loss. Physical examination reveals clear lung fields bilaterally. Vital signs are stable with SpO2 92% on room air at rest. Laboratory studies show serum calcium 11.8 mg/dL (normal 8.5-10.5), elevated angiotensin-converting enzyme (ACE) at 72 U/L, and normal liver and renal function. Chest radiograph demonstrates bilateral hilar lymphadenopathy with clear lung parenchyma and no evidence of pulmonary fibrosis. Pulmonary function tests show FVC 75% predicted, FEV1 78% predicted, FEV1/FVC ratio 93% (normal), and DLCO 58% predicted. Which of the following best explains the disproportionately reduced DLCO relative to the preservation of spirometric lung volumes?

1. A)Granulomatous inflammation and infiltration of the alveolar-capillary membraneGABARITO
2. B)Endobronchial granulomas causing small airway obstruction with air trapping
3. C)Cardiac involvement with reduced pulmonary capillary blood flow
4. D)Mediastinal lymphadenopathy compressing the pulmonary veins
5. E)Respiratory muscle involvement limiting maximal inspiration effort