This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Obstetrics, Subject name: Gynaecology & Obstetrics
[{'content': 'Hormone responsible for decidual reaction and arias Stella reaction in ectopic pregnancy is - \nSelect and explain. \nA. Oestrogen, B. Progesterone, C. HCG, D. HPL', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Hormone responsible for decidual reaction and arias Stella reaction in Ectopic as well as Intrauterine pregnancy is Progesterone Arias stella reaction is the localized hypersecretory endometrium seen in ectopic pregnancy.', 'role': 'assistant'}]