Fact 1: Fertilization occurs when a sperm and an egg fuse.

Fact 2: Fertilization As far as fertilization, timing is critical.

Given the two facts above, answer the question "When is timing critical?" with the following options: 
- a hemisphere is tilted away from the sun
 - object is kicked
 - movement of tectonic plates
 - flow of electrons
 - when the sperm and egg fuse
 - Earth revolving around the sun
 - Warm air moving into cold air
 - seed dispersal


 

     when the sperm and egg fuse    