This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Medicine
Carbon monoxide diffusion capacity decreases in all, Except - 
Select and explain. 
A. Emphysema, B. Primary pulmonary hypertension, C. Alveolar haemorrhage, D. Infiltrative lung disease
C: Alveolar haemorrhage
Answer: C: Alveolar haemorrhage 
Explanation: None