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
Which one of the following investigations is considered to be "Gold standard" technique for diagnosis of arterial occlusive disease – 
Select and explain. 
A. Doppler ultrasound blood flow detection, B. Duplex imaging, C. Treadmill, D. Digital substraction angiography (DSA)
D: Digital substraction angiography (DSA)
Answer: D: Digital substraction angiography (DSA) 
Explanation: None