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
The hormone responsible for the decidual and Arias stella reaction of ectopic pregnancy is : 
Select and explain. 
A. HCG, B. Progesterone, C. Estrogen, D. HPL
B: Progesterone
Answer: B: Progesterone 
Explanation: Progesterone