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

Fact 2: Sperm and eggs are cells known as gametes.

Given the two facts above, answer the question "What causes fertilization?" with the following options: 
- pollen
 - infertility
 - gametes
 - orchids
 - seeds
 - no physical contact
 - honeybees
 - isolation


 

   gametes      