Why Does the Surface of the Oocyte Change When the First

Why does the surface of the oocyte change when the first sperm cell touches the secondary oocyte?

A) to prevent the first sperm from further entering the egg before more of the outer layer of follicle cells is penetrated by other sperm
B) to prevent the first sperm from fertilizing the egg until the uterus is prepared for implantation
C) to allow the first sperm to enter the egg and fertilization to occur
D) to allow up to 200 sperm to enter the egg,though only one sperm will fertilize the egg
E) to prevent more than one sperm from entering the egg