Fertilization occurs when a sperm and an egg fuse, and fertilization As far as fertilization, timing is critical. Given these facts, when is timing critical among the following options:
- for gravity
 - Warm air moving into cold air
 - earth's orbit
 - when sperm and egg fuse
 - flow of electrons
 - earth's rotation
 - Earth revolving around the sun
 - movement of tectonic plates


 

    when sperm and egg fuse     