This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Hypeension, Subject name: Medicine
A patient with recent loss of hypeension control and creatinine- 4.2 mg/dL. Renal USG shows size discrepancy in kidneys and no sign of obstruction .What should be the next investigation ? 
Select and explain. 
A. IVP, B. MR angiography, C. Retrograde pyelography, D. Ultasound Doppler
D: Ultasound Doppler
Answer: D: Ultasound Doppler 
Explanation: As patient has history of loss of control of hypeension and raised creatinine , Renal USG is warranted . USG findings and clinical history raise suspicion of Renovascular hypeension . Next Investigation of choice is Ultrasound Doppler as it confirms diagnosis of Renovascular hypeension in vasculature .