This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory system, Subject name: Medicine
The most definitive method of diagnosing pulmonary embolism is 
Select and explain. 
A. Pulmonary ateriography, B. Radioisotope perfusion pulmonary scintigraphy, C. EKG, D. Venography
A: Pulmonary ateriography
Answer: A: Pulmonary ateriography 
Explanation: Pulmonary aeriography is the most definitive method of diagnosing pulmonary embolism.Chest CT with contrast has viually replaced invasive pulmonary angiography as a diagnostic test.A definitive diagnosis of PE depends on visualisation of an intraluminal filling defect in more than one projection.Secondary signs of PE include abrupt occlusion("cut-off") of vessels,segmental oligemia or avascularity,a prolonged aerial phase with slow filling,and touous,tapering peripheral vessels. Reference:Harrison's medicine-18th edition,page no:2174.