This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General obstetrics, Subject name: Gynaecology & Obstetrics
Zona hatching occurs 
Select and explain. 
A. 4 days after feilisation, B. 5 days after feilisation, C. 6 days after feilisation, D. 8 days after feilisation
B: 5 days after feilisation
Answer: B: 5 days after feilisation 
Explanation: Five days after feilisation, blastocyst performs zona hatching and it undergoes degeneration to be replaced by trophoblastic cells