Fertilization occurs when a sperm and an egg fuse to form a diploid zygote, and penetration is when the sperm and egg meet and the sperm makes it way into the egg cytoplasm. Given these facts, what requires penetration among the following options:
- gravity
 - weathering
 - gastropod shells
 - the skin
 - an object
 - death
 - Veins and arteries.
 - fertilization


 

        fertilization 