This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Contraception, Subject name: Gynaecology & Obstetrics
[{'content': 'The progestin present in Sino-Implant II is \nSelect and explain. \nA. Etonogestrel, B. Levonorgestrel, C. Norethisterone, D. Desogestrel', 'role': 'user'}, {'content': "Answer: B \nExplanation: The Sino-Implant II is a less expensive two-rod levonorgestrel system manufactured in China and available in several countries. It is effective for 4 yearsReference: Novak's gynaecology; 14th edition; Chapter 10; Family planning", 'role': 'assistant'}]