Immunocontraception Is Where the Immune System Is Induced to Make

Immunocontraception is where the immune system is induced to make antibodies to attack particular proteins involved in fertility. What is one such protein being looked at for this purpose?

A) Testosterone
B) The precursor protein for estrogen
C) The protein in an egg membrane that allows the sperm in
D) The protein that makes sperm cell tails wiggle strongly enough to get into an egg.
E) The protein that makes sperm cell tails wiggle strongly enough to swim.