The Chorionic Villi

The chorionic villi

A) help prepare the mammary glands for milk production.
B) are free endodermal tips that grow toward the wall of the blastocyst.
C) bulge into the amniotic cavity at the head fold and extend toward the trophoblast.
D) provide the surface area for gaseous exchange between fetal and maternal bloodstreams.
E) form constrictions that narrow the yolk stalk and the body stalk between the embryo and the surrounding trophoblast.