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
Most important sign in hemodynamically significant renal artery stenosis 
Select and explain. 
A. Presence of collateral vessels, B. Elevated renin level in I/L renal vein  ≥  1.5 : 1, C. Transstenotic pressure gradient  ≥ 40 mm Hg, D. Decrease in renal size
A: Presence of collateral vessels
Answer: A: Presence of collateral vessels 
Explanation: All are signs of renal artery stenosis.
Most  important - Presence of collateral vessels.