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': 'The hormone responsible for the decidual and Arias stella reaction of ectopic pregnancy is : \nSelect and explain. \nA. HCG, B. Progesterone, C. Estrogen, D. HPL', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Progesterone', 'role': 'assistant'}]