Fact 1: Fertilization occurs when a sperm and an egg fuse to form a diploid zygote.

Fact 2: Penetration is when the sperm and egg meet and the sperm makes it way into the egg cytoplasm.

Given the two facts above, answer the question "what requires penetration?" with the following options: 
- gravity
 - weathering
 - gastropod shells
 - the skin
 - an object
 - death
 - Veins and arteries.
 - fertilization


 

        fertilization 