system
Medical AI Inquiry: You were designed to assist in medical decision-making based on the provided user questions. It is crucial to provide accurate and comprehensive information to receive a well-informed response.
user
Implantation occurs at the stage of
assistant
The correct answer is  C i.e. Blastocyst- Barrier is provided by fusion / feilin (not Ach)Q. Fusion reduce the membrane potential of ovum that prevents polyspermy by not allowing the others sperms to enter.- Morula is a 16 cell stage, surrounded by zona pellucida. Barrier is provided by fusiotVfetilin.QImplantation occurs at the stage of blasto cystQ.