This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrinology, Subject name: Physiology
By the time of implantation in uterine endometrium the typical feilized ovum is divided into how many cells 
Select and explain. 
A. 2, B. 4, C. 16, D. 750
C: 16
Answer: C: 16 
Explanation: Implantation is the attachment of the blastocyst to the endometrium, and its subsequent embedding in the compact layer, occurring 6-7 days after feilization of the oocyte in humans. Blastocyst is a pre-implantation embryo consisting of a thin-walled hollow sphere of 16-32 cells, which appears in early mammalian development, the wall of which is the trophoblast.Ref: Ganong&;s review of medical physiology; 24th edition; page no:-413