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: Gynaecology & Obstetrics
[{'content': 'Which one of the following is longest acting IUCD: \nSelect and explain. \nA. Progestase, B. Cu -- T -- 380, C. Mirena, D. Norgesterol', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Cu -- T -- 380', 'role': 'assistant'}]