You are presented with the question "When is timing critical?" and the following answer choices: 
- 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

Now knowing that fertilization occurs when a sperm and an egg fuse and fertilization As far as fertilization, timing is critical, choose the best answer.


 

     when the sperm and egg fuse    