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': "In the etiology of endometriosis Sampson's theory is : \nSelect and explain. \nA. Implantation theory, B. Coelomic metaplasia theory, C. Metastatic theory, D. Histogenesis by induction", 'role': 'user'}, {'content': 'Answer: A \nExplanation: Implantation theory', 'role': 'assistant'}]