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: Surgery
[{'content': 'After a single episode of painless gross hematuria in a boy. Doctor performed an excretory urogram showing a filling defect towards the lower renal infundibulum 1.5 cm. in size. What will be the next investigation to be done - \nSelect and explain. \nA. Cystoscopy, B. Urine cytology, C. USG, D. Retrograde pyelography', 'role': 'user'}, {'content': 'Answer: C \nExplanation: There can be various reason for a filling defect on IVP - stones, mass, cyst etc.\nThey can be very well be diagnosed by USG.', 'role': 'assistant'}]