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
The substance used in OCG is - 
Select and explain. 
A. Iapanoic acid, B. Sodium diatrozite, C. Meglumine iodothalamate, D. Biligraffin
A: Iapanoic acid
Answer: A: Iapanoic acid 
Explanation: Ans. is 'a' i.e. Iapanoic acid