The correct option is B The embryo is drawn into the placenta and becomes surrounded by it
Implantation is the process by which the embryo gets embedded in the folds of the endometrium. After implantation, finger-like projections appear on the trophoblast called chorionic villi which are surrounded by the uterine tissue and maternal
blood. During this process the embryo gets surrounded by hollow ball. Placenta does not surround the embryo.