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': 'True about OCG is : \nSelect and explain. \nA. First done by Graham Cole in 1942, B. Dye ingested at rate of 1 ml/kg, C. USG has replaced it, D. All', 'role': 'user'}, {'content': 'Answer: C \nExplanation: C i.e. USG has replaced it', 'role': 'assistant'}]