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
[{'content': 'In Renal cell carcinoma investigation of choice to evaluate inferior venacava & renal vein for thrombus \nSelect and explain. \nA. IVP, B. Coloured Doppler, C. USG, D. CT scan', 'role': 'user'}, {'content': 'Answer: B \nExplanation: B i.e. Coloured Doppler', 'role': 'assistant'}]