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: Anatomy
Implantation occurs at the stage of - 
Select and explain. 
A. Zygote, B. Morula, C. Blastocyst, D. Primary villi
C: Blastocyst
Answer: C: Blastocyst 
Explanation: None