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: Radiology
A 55-year-old man, who has been on bed rest for the past 10 days, complains of breathlessness and chest pain. The chest X-ray is normal. The next step in investigation should he: 
Select and explain. 
A. I.ung ventilation - perfusion scan, B. Pulmonary aeriography, C. Pulmonary venous wedge angiography, D. Echocardiography
A: I.ung ventilation - perfusion scan
Answer: A: I.ung ventilation - perfusion scan 
Explanation: Ans. I.ung ventilation - perfusion scan