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
True about OCG is : 
Select and explain. 
A. First done by Graham Cole in 1942, B. Dye ingested at rate of 1 ml/kg, C. USG has replaced it, D. All
C: USG has replaced it
Answer: C: USG has replaced it 
Explanation: C i.e. USG has replaced it