Answer:
When an egg is fertilized, it divides into two components — one becomes the embryo, which develops into the fetus, and the other becomes the placenta, which grows along the lining of the uterus. The umbilical cord develops from embryonic tissue and will grow about 60 centimetres long.
The umbilical cord develops from and contains remnants of the yolk sac and allantois. It forms by the fifth week of development, replacing the yolk sac as the source of nutrients for the embryo.
OR put simply
A, the oyster cells of the blastocyst.
