The Embryo Becomes Implanted in the Endometrium of the Uterus

The embryo becomes implanted in the endometrium of the uterus due to

A) special receptors on the endometrium to which the blastocyst attaches.
B) enzymes secreted by the trophoblast, which erode an area of the endometrium for entry of the embryo.
C) special phagocytic cells in the endometrium, which engulf the embryo.
D) the sticky coat of the zona pellucida, which adheres to the endometrium.
E) the action of hCG secreted by the embryo.