Once Diffusion from the Endometrium Becomes Inadequate for Delivery of Oxygen

Once diffusion from the endometrium becomes inadequate for delivery of oxygen, the placenta develops from projections of the______, which facilitates exchange of nutrients and waste by the______

A) amnionic villi into the endometrium : short distance between maternal and fetal blood
B) chorionic villi into the embryo : mixing of maternal and fetal blood
C) chorionic villi into the endometrium : short distance between maternal and fetal blood
D) chorionic villi into the endometrium : mixing of maternal and fetal blood
E) chorionic villi into the embryo : short distance between maternal and fetal blood