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': 'Green coloured i.v. cannula, the size is \nSelect and explain. \nA. 18, B. 20, C. 22, D. 24', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Answer- A. 18Green- 18Pink- 20Blue- 22Yellow/lime- 24', 'role': 'assistant'}]