Question

what prevents polyspermy from occurring?
a the secondary oocyte plasma membrane depolarizes.
b the zona pellucida chemically changes into the fertilization membrane.
c only one sperm can normally enter the zona pellucida.
d both the secondary oocyte plasma membrane depolarizes and the zona pellucida chemically changes into the fertilization membrane are correct.

Explanation:

Polyspermy is prevented by two mechanisms. The fast block is the depolarization of the secondary oocyte plasma membrane. The slow block is the chemical change of the zona pellucida into the fertilization membrane.

Answer:

D. Both the secondary oocyte plasma membrane depolarizes and the zona pellucida chemically changes into the fertilization membrane are correct.