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
In a patient with renal cell carcinoma with a thrombus in the IVCrenal vein, which of the following is the best for diagnosis? 
Select and explain. 
A. CT scan, B. Angiography, C. Colour Doppler imaging, D. IVP
A: CT scan
Answer: A: CT scan 
Explanation: Ans. CT scan