This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Pathology
When does the Implantation occur? 
Select and explain. 
A. On day 4 after feilization, B. After the endometrium undergoes a decidual reaction, C. When the embryo is at the morula stage, D. Only after priming of the uterine endometrium by progesterone and estrogen
D: Only after priming of the uterine endometrium by progesterone and estrogen
Answer: D: Only after priming of the uterine endometrium by progesterone and estrogen 
Explanation: .